Narrowband time-division duplex frame structure for narrowband communications

ABSTRACT

There is a need to support narrowband TDD frame structure for narrowband communications. The present disclosure provides a solution by supporting one or more narrowband TDD frame structure(s) for narrowband communications. In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may determine a narrowband TDD frame structure for narrowband communications from a group of narrowband TDD frame structures. In one aspect, the narrowband TDD frame structure may include a set of downlink subframes and more than one special subframe. The apparatus may determine a set of narrowband carriers and a minimum set of subframes on the set of narrowband carriers based at least in part on the set of downlink subframes and more than one special subframe on which a NRS should be transmitted. The apparatus may transmit the NRS using the narrowband TDD frame structure determined for the narrowband communications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Indian Application Serial No.201741005220, entitled “NARROWBAND TIME-DIVISION DUPLEX FRAME STRUCTUREFOR NARROWBAND COMMUNICATIONS” and filed on Feb. 14, 2017, which isexpressly incorporated by reference herein in its entirety. In addition,this application claims the benefit of Indian Application Serial No.201741005360, entitled “NARROWBAND TIME-DIVISION DUPLEX FRAME STRUCTUREFOR NARROWBAND COMMUNICATIONS” and filed on Feb. 15, 2017, which isexpressly incorporated by reference herein in its entirety.

BACKGROUND Field

The present disclosure relates generally to communication systems, andmore particularly, to a narrowband time-division duplex (TDD) framestructure for narrowband communications.

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis 5G New Radio (NR). 5G NR is part of a continuous mobile broadbandevolution promulgated by Third Generation Partnership Project (3GPP) tomeet new requirements associated with latency, reliability, security,scalability (e.g., with Internet of Things (IoT)), and otherrequirements. Some aspects of 5G NR may be based on the 4G Long TermEvolution (LTE) standard. There exists a need for further improvementsin 5G NR technology. These improvements may also be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

Narrowband communications involve communicating with a limited frequencybandwidth as compared to the frequency bandwidth used for LTEcommunications. One example of narrowband communication is narrowband(NB) IoT (NB-IoT) communication, which is limited to a single resourceblock (RB) of system bandwidth, e.g., 180 kHz. Another example ofnarrowband communication is enhanced machine-type communication (eMTC),which is limited to six RBs of system bandwidth, e.g., 1.08 MHz.

NB-IoT communication and eMTC may reduce device complexity, enablemulti-year battery life, and provide deeper coverage to reachchallenging locations such as deep inside buildings. Because thecoverage provided by narrowband communications may include reachingchallenging locations (e.g., a smart gas meter located in the basementof a building) there is an increased chance that one or moretransmissions will not be properly received. Hence, repeatedtransmissions may be used in narrowband communication to increase theprobability that a transmission will be properly decoded by a receiverdevice. A TDD frame structure may support repeated transmissions due toan increased number of contiguous downlink and/or uplink subframes, ascompared to a frequency division-duplex (FDD) frame structure. There isa need to support narrowband TDD frame structure for narrowbandcommunication.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

Narrowband communications involve communicating with a limited frequencybandwidth as compared to the frequency bandwidth used for LTEcommunications. One example of narrowband communication is NB-IoTcommunication, which is limited to a single RB of system bandwidth,e.g., 180 kHz. Another example of narrowband communication is eMTC,which is limited to six RBs of system bandwidth, e.g., 1.08 MHz.

NB-IoT communication and eMTC may reduce device complexity, enablemulti-year battery life, and provide deeper coverage to reachchallenging locations such as deep inside buildings. However, becausethe coverage provided by narrowband communications may include reachingchallenging locations (e.g., a smart gas meter located in the basementof a building) there is an increased chance that one or moretransmissions will not be properly decoded by a receiver device.Consequently, narrowband communication may include a predeterminednumber of repeated transmissions to increase the chance of having thetransmission properly decoded by the receiver device. A TDD framestructure may be used by a narrowband communication system since certainTDD frame configurations may include a greater number of contiguousuplink and/or downlink subframes that may be used for the repeatedtransmissions, as compared to a FDD frame structure. There is a need tosupport the use of narrowband TDD frame structure for narrowbandcommunication.

The present disclosure provides a mechanism to support one or morenarrowband TDD frame structure(s) for narrowband communication.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided. The apparatus may determine a bandwidthfor narrowband communications. The apparatus may determine a narrowbandTDD frame structure for the narrowband communications. In one aspect,the narrowband TDD frame structure may include at least one of two ormore contiguous downlink subframes, or one or more flexible subframesthat can be configured as either a downlink subframe or an uplinksubframe. The apparatus may communicate with a UE using the narrowbandTDD frame structure determined for the narrowband communications.

In certain aspects, the apparatus may determine a TDD mode fornarrowband communications. The apparatus may also determine a TDD framestructure for the narrowband communications from a group of narrowbandTDD frame structures. In an aspect, at least one common subframe in eachnarrowband TDD frame structure in the group of narrowband TDD framestructures may be configured as a downlink subframe. The apparatus mayalso transmit a primary synchronization signal (PSS) using the at leastone common subframe in the narrowband TDD frame structure determined forthe narrowband communications.

In certain other aspects, the apparatus may determine a TDD mode fornarrowband communications. The apparatus may also determine a narrowbandTDD frame structure for the narrowband communications from a group ofnarrowband TDD frame structures. The apparatus may also transmit a PSSusing the narrowband TDD frame structure determined for the narrowbandcommunications. In an aspect, a set of PSS sequences may be associatedwith at least one of the TDD mode or the narrowband TDD frame structuredetermined for the narrowband communications.

In certain other aspects, the apparatus may determine a narrowbandcommunication frame structure comprising a FDD mode or a TDD mode and aparticular TDD frame structure for narrowband communications from agroup of narrowband TDD frame structures. The apparatus may determine aperiodicity, subframe number, and transmission sequence associated witha SSS based at least in part on the narrowband TDD frame structure. Theapparatus may transmit the SSS using the narrowband TDD frame structuredetermined for the narrowband communications. In one aspect, the SSS maybe transmitted using a same subframe in at most every other frame.

In certain other aspects, the apparatus may determine a narrowbandcommunication frame structure comprising a FDD frame structure or a TDDframe structure and a narrowband TDD frame structure configuration fornarrowband communications from a group of narrowband TDD framestructures configurations. The apparatus may determine one or morenarrowband carriers and subframes within the one or more narrowbandcarriers to transmit at least one of a BCH or a SIB1 based on thenarrowband communication frame structure or the TDD frame structureconfiguration. The apparatus may transmit a PSS, an SSS, and at leastone of a BCH or an SIB1 using the narrowband TDD frame structuredetermined for the narrowband communications. In one aspect, a carrierused for transmitting the BCH and/or the SIB may be different than acarrier used to transmit one or more of the PSS or the SSS. In anotheraspect, a narrowband carrier used for transmitting the BCH may bedifferent than a narrowband carrier used to transmit one or more of thePSS or the SSS.

In certain other aspects, the apparatus may determine a narrowband TDDframe structure for narrowband communications. In one aspect, thenarrowband TDD frame structure may include one or more of a set ofdownlink subframes, a set of uplink subframes, a set of specialsubframes, or a set of flexible subframes. In certain other aspects, theapparatus may transmit a bitmap associated with the narrowband TDD framestructure to a UE. In one aspect, the bitmap may indicate the one ormore of the set of downlink subframes, the set of uplink subframes, theset of special subframes, or the set of flexible subframes.

The apparatus may determine a narrowband TDD frame structure fornarrowband communications from a group of narrowband TDD framestructures. In one aspect, the narrowband TDD frame structure mayinclude a set of downlink subframes and more than one special subframe.The apparatus may determine a set of narrowband carriers and a minimumset of subframes on the set of narrowband carriers based at least inpart on the set of downlink subframes and more than one special subframeon which a NRS should be transmitted. The apparatus may transmit the NRSusing the narrowband TDD frame structure determined for the narrowbandcommunications.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating LTE examples of a DLframe structure, DL channels within the DL frame structure, an UL framestructure, and UL channels within the UL frame structure, respectively.

FIG. 3 is a diagram illustrating an example of an evolved Node B (eNB)and user equipment (UE) in an access network.

FIG. 4 is a diagram illustrating example narrowband TDD frame structuresin accordance with certain aspects of the disclosure.

FIG. 5A is a diagram of a dataflow for narrowband communications usingnarrowband TDD frame structures in accordance with certain aspects ofthe disclosure.

FIGS. 5B-5D are a diagram of a dataflow for narrowband communicationsusing narrowband TDD frame structures in accordance with certain aspectsof the disclosure.

FIG. 6 is a flowchart of a method of wireless communication.

FIG. 7 is a flowchart of a method of wireless communication.

FIG. 8 is a flowchart of a method of wireless communication.

FIG. 9 is a flowchart of a method of wireless communication.

FIG. 10 is a flowchart of a method of wireless communication.

FIG. 11 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 12 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 13 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 14 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 15 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 16 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 17 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 18 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 19 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 20 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 21 is a diagram of a dataflow for narrowband communications usingnarrowband TDD frame structures in accordance with certain aspects ofthe disclosure.

FIG. 22 is a flowchart of a method of wireless communication.

FIG. 23 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 24 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 25 is a flowchart of a method of wireless communication.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, and an Evolved Packet Core (EPC) 160. The basestations 102 may include macro cells (high power cellular base station)and/or small cells (low power cellular base station). The macro cellsinclude base stations. The small cells include femtocells, picocells,and microcells.

The base stations 102 (collectively referred to as Evolved UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access Network(E-UTRAN)) interface with the EPC 160 through backhaul links 132 (e.g.,51 interface). In addition to other functions, the base stations 102 mayperform one or more of the following functions: transfer of user data,radio channel ciphering and deciphering, integrity protection, headercompression, mobility control functions (e.g., handover, dualconnectivity), inter-cell interference coordination, connection setupand release, load balancing, distribution for non-access stratum (NAS)messages, NAS node selection, synchronization, radio access network(RAN) sharing, multimedia broadcast multicast service (MBMS), subscriberand equipment trace, RAN information management (RIM), paging,positioning, and delivery of warning messages. The base stations 102 maycommunicate directly or indirectly (e.g., through the EPC 160) with eachother over backhaul links 134 (e.g., X2 interface). The backhaul links134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacro cells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (alsoreferred to as forward link) transmissions from a base station 102 to aUE 104. The communication links 120 may use multiple-input andmultiple-output (MIMO) antenna technology, including spatialmultiplexing, beamforming, and/or transmit diversity. The communicationlinks may be through one or more carriers. The base stations 102/UEs 104may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100 MHz) bandwidthper carrier allocated in a carrier aggregation of up to a total of YxMHz (x component carriers) used for transmission in each direction. Thecarriers may or may not be adjacent to each other. Allocation ofcarriers may be asymmetric with respect to downlink and uplink (e.g.,more or less carriers may be allocated for downlink than for uplink).The component carriers may include a primary component carrier and oneor more secondary component carriers. A primary component carrier may bereferred to as a primary cell (PCell) and a secondary component carriermay be referred to as a secondary cell (SCell).

Certain UEs 104 may communicate with each other using device-to-device(D2D) communication link 192. The D2D communication link 192 may use theDL/UL WWAN spectrum. The D2D communication link 192 may use one or moresidelink channels, such as a physical sidelink broadcast channel(PSBCH), a physical sidelink discovery channel (PSDCH), a physicalsidelink shared channel (PSSCH), and a physical sidelink control channel(PSCCH). D2D communication may be through a variety of wireless D2Dcommunications systems, such as for example, FlashLinQ, WiMedia,Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ NR and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing NR in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network.

The gNodeB (gNB) 180 may operate in millimeter wave (mmW) frequenciesand/or near mmW frequencies in communication with the UE 104. When thegNB 180 operates in mmW or near mmW frequencies, the gNB 180 may bereferred to as an mmW base station. Extremely high frequency (EHF) ispart of the RF in the electromagnetic spectrum. EHF has a range of 30GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters.Radio waves in the band may be referred to as a millimeter wave. NearmmW may extend down to a frequency of 3 GHz with a wavelength of 100millimeters. The super high frequency (SHF) band extends between 3 GHzand 30 GHz, also referred to as centimeter wave. Communications usingthe mmW/near mmW radio frequency band has extremely high path loss and ashort range. The mmW base station 180 may utilize beamforming 184 withthe UE 104 to compensate for the extremely high path loss and shortrange.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMEs 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService, and/or other IP services. The BM-SC 170 may provide functionsfor MBMS user service provisioning and delivery. The BM-SC 170 may serveas an entry point for content provider MBMS transmission, may be used toauthorize and initiate MBMS Bearer Services within a public land mobilenetwork (PLMN), and may be used to schedule MBMS transmissions. The MBMSGateway 168 may be used to distribute MBMS traffic to the base stations102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN)area broadcasting a particular service, and may be responsible forsession management (start/stop) and for collecting eMBMS relatedcharging information.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), or some other suitableterminology. The base station 102 provides an access point to the EPC160 for a UE 104. Examples of UEs 104 include a cellular phone, a smartphone, a session initiation protocol (SIP) phone, a laptop, a personaldigital assistant (PDA), a satellite radio, a global positioning system,a multimedia device, a video device, a digital audio player (e.g., MP3player), a camera, a game console, a tablet, a smart device, a wearabledevice, a vehicle, an electric meter, a gas pump, a toaster, or anyother similar functioning device. Some of the UEs 104 may be referred toas IoT devices (e.g., parking meter, gas pump, toaster, vehicles, etc.).The UE 104 may also be referred to as a station, a mobile station, asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal, a mobile terminal, a wireless terminal, a remoteterminal, a handset, a user agent, a mobile client, a client, or someother suitable terminology.

Referring again to FIG. 1, in certain aspects, the base station 102, 180and/or UE 104 may be configured to support one or more narrowband TDDframe structure(s) for narrowband communications (198), e.g., asdescribed in connection with any of FIGS. 4-25.

FIG. 2A is a diagram 200 illustrating an example of a DL frame structurein LTE. FIG. 2B is a diagram 230 illustrating an example of channelswithin the DL frame structure in LTE. FIG. 2C is a diagram 250illustrating an example of an UL frame structure in LTE. FIG. 2D is adiagram 280 illustrating an example of channels within the UL framestructure in LTE. Other wireless communication technologies may have adifferent frame structure and/or different channels. In LTE, a frame (10ms) may be divided into 10 equally sized subframes. Each subframe mayinclude two consecutive time slots. A resource grid may be used torepresent the two time slots, each time slot including one or more timeconcurrent resource blocks (RBs) (also referred to as physical RBs(PRBs)). The resource grid is divided into multiple resource elements(REs). In LTE, for a normal cyclic prefix, an RB contains 12 consecutivesubcarriers in the frequency domain and 7 consecutive symbols (for DL,OFDM symbols; for UL, SC-FDMA symbols) in the time domain, for a totalof 84 REs. For an extended cyclic prefix, an RB contains 12 consecutivesubcarriers in the frequency domain and 6 consecutive symbols in thetime domain, for a total of 72 REs. The number of bits carried by eachRE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry DL reference (pilot)signals (DL-RS) for channel estimation at the UE. The DL-RS may includecell-specific reference signals (CRS) (also sometimes called common RS),UE-specific reference signals (UE-RS), and channel state informationreference signals (CSI-RS). FIG. 2A illustrates CRS for antenna ports 0,1, 2, and 3 (indicated as R₀, R₁, R₂, and R₃, respectively), UE-RS forantenna port 5 (indicated as R₅), and CSI-RS for antenna port 15(indicated as R). FIG. 2B illustrates an example of various channelswithin a DL subframe of a frame. The physical control format indicatorchannel (PCFICH) is within symbol 0 of slot 0, and carries a controlformat indicator (CFI) that indicates whether the physical downlinkcontrol channel (PDCCH) occupies 1, 2, or 3 symbols (FIG. 2B illustratesa PDCCH that occupies 3 symbols). The PDCCH carries downlink controlinformation (DCI) within one or more control channel elements (CCEs),each CCE including nine RE groups (REGs), each REG including fourconsecutive REs in an OFDM symbol. A UE may be configured with aUE-specific enhanced PDCCH (ePDCCH) that also carries DCI. The ePDCCHmay have 2, 4, or 8 RB pairs (FIG. 2B shows two RB pairs, each subsetincluding one RB pair). The physical hybrid automatic repeat request(ARQ) (HARQ) indicator channel (PHICH) is also within symbol 0 of slot 0and carries the HARQ indicator (HI) that indicates HARQ acknowledgement(ACK)/negative ACK (NACK) feedback based on the physical uplink sharedchannel (PUSCH). The primary synchronization channel (PSCH) is withinsymbol 6 of slot 0 within subframes 0 and 5 of a frame, and carries aPSS that is used by a UE to determine subframe timing and a physicallayer identity. The secondary synchronization channel (SSCH) is withinsymbol 5 of slot 0 within subframes 0 and 5 of a frame, and carries anSSS that is used by a UE to determine a physical layer cell identitygroup number. Based on the physical layer identity and the physicallayer cell identity group number, the UE can determine a physical cellidentifier (PCI). Based on the PCI, the UE can determine the locationsof the aforementioned DL-RS. The physical broadcast channel (PBCH) iswithin symbols 0, 1, 2, 3 of slot 1 of subframe 0 of a frame, andcarries a master information block (MIB). The MIB provides a number ofRBs in the DL system bandwidth, a PHICH configuration, and a systemframe number (SFN). The physical downlink shared channel (PDSCH) carriesuser data, broadcast system information not transmitted through the PBCHsuch as system information blocks (SIBs), and paging messages.

As illustrated in FIG. 2C, some of the REs carry demodulation referencesignals (DM-RS) for channel estimation at the eNB. The UE mayadditionally transmit sounding reference signals (SRS) in the lastsymbol of a subframe. The SRS may have a comb structure, and a UE maytransmit SRS on one of the combs. The SRS may be used by an eNB forchannel quality estimation to enable frequency-dependent scheduling onthe UL. FIG. 2D illustrates an example of various channels within an ULsubframe of a frame. A physical random access channel (PRACH) may bewithin one or more subframes within a frame based on the PRACHconfiguration. The PRACH may include six consecutive RB pairs within asubframe. The PRACH allows the UE to perform initial system access andachieve UL synchronization. A physical uplink control channel (PUCCH)may be located on edges of the UL system bandwidth. The PUCCH carriesuplink control information (UCI), such as scheduling requests, a channelquality indicator (CQI), a precoding matrix indicator (PMI), a rankindicator (RI), and HARQ ACK/NACK feedback. The PUSCH carries data, andmay additionally be used to carry a buffer status report (BSR), a powerheadroom report (PHR), and/or UCI.

FIG. 3 is a block diagram of an eNB 310 in communication with a UE 350in an access network. In the DL, IP packets from the EPC 160 may beprovided to a controller/processor 375. The controller/processor 375implements layer 3 and layer 2 functionality. Layer 3 includes a radioresource control (RRC) layer, and layer 2 includes a packet dataconvergence protocol (PDCP) layer, a radio link control (RLC) layer, anda medium access control (MAC) layer. The controller/processor 375provides RRC layer functionality associated with broadcasting of systeminformation (e.g., MIB, SIBs), RRC connection control (e.g., RRCconnection paging, RRC connection establishment, RRC connectionmodification, and RRC connection release), inter radio access technology(RAT) mobility, and measurement configuration for UE measurementreporting; PDCP layer functionality associated with headercompression/decompression, security (ciphering, deciphering, integrityprotection, integrity verification), and handover support functions; RLClayer functionality associated with the transfer of upper layer packetdata units (PDUs), error correction through ARQ, concatenation,segmentation, and reassembly of RLC service data units (SDUs),re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto transport blocks(TBs), demultiplexing of MAC SDUs from TBs, scheduling informationreporting, error correction through HARQ, priority handling, and logicalchannel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 316 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 374 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 350. Each spatial stream may then be provided to a differentantenna 320 via a separate transmitter 318TX. Each transmitter 318TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 350, each receiver 354RX receives a signal through itsrespective antenna 352. Each receiver 354RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 356. The TX processor 368 and the RX processor 356implement layer 1 functionality associated with various signalprocessing functions. The RX processor 356 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 350. If multiple spatial streams are destined for the UE 350,they may be combined by the RX processor 356 into a single OFDM symbolstream. The RX processor 356 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe eNB 310. These soft decisions may be based on channel estimatescomputed by the channel estimator 358. The soft decisions are thendecoded and deinterleaved to recover the data and control signals thatwere originally transmitted by the eNB 310 on the physical channel. Thedata and control signals are then provided to the controller/processor359, which implements layer 3 and layer 2 functionality.

The controller/processor 359 can be associated with a memory 360 thatstores program codes and data. The memory 360 may be referred to as acomputer-readable medium. In the UL, the controller/processor 359provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing to recover IP packets from the EPC 160. Thecontroller/processor 359 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the eNB 310, the controller/processor 359 provides RRClayer functionality associated with system information (e.g., MIB, SIBs)acquisition, RRC connections, and measurement reporting; PDCP layerfunctionality associated with header compression/decompression, andsecurity (ciphering, deciphering, integrity protection, integrityverification); RLC layer functionality associated with the transfer ofupper layer PDUs, error correction through ARQ, concatenation,segmentation, and reassembly of RLC SDUs, re-segmentation of RLC dataPDUs, and reordering of RLC data PDUs; and MAC layer functionalityassociated with mapping between logical channels and transport channels,multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs,scheduling information reporting, error correction through HARQ,priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 358 from a referencesignal or feedback transmitted by the eNB 310 may be used by the TXprocessor 368 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 368 may be provided to different antenna 352 viaseparate transmitters 354TX. Each transmitter 354TX may modulate an RFcarrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB 310 in a manner similar tothat described in connection with the receiver function at the UE 350.Each receiver 318RX receives a signal through its respective antenna320. Each receiver 318RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 thatstores program codes and data. The memory 376 may be referred to as acomputer-readable medium. In the UL, the controller/processor 375provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 350. IP packets from thecontroller/processor 375 may be provided to the EPC 160. Thecontroller/processor 375 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Narrowband communications involve communicating with a limited frequencybandwidth as compared to the frequency bandwidth used for LTEcommunications. One example of narrowband communication is NB-IoTcommunication, which is limited to a single RB of system bandwidth,e.g., 180 kHz. Another example of narrowband communication is eMTC,which is limited to six RBs of system bandwidth, e.g., 1.08 MHz.

NB-IoT communication and eMTC may reduce device complexity, enablemulti-year battery life, and provide deeper coverage to reachchallenging locations such as deep inside buildings. However, becausethe coverage provided by narrowband communications may include reachingchallenging locations (e.g., a smart gas meter located in the basementof a building) there is an increased chance that one or moretransmissions will not be properly decoded by a receiver device.Consequently, narrowband communication may include a predeterminednumber of repeated transmissions to increase the chance of having thetransmission properly decoded by the receiver device. A TDD framestructure may be used by a narrowband communication system since certainTDD frame configurations may include a greater number of contiguousuplink and/or downlink subframes that may be used for the repeatedtransmissions, as compared to a FDD frame structure. There is a need tosupport the use of narrowband TDD frame structure for narrowbandcommunication.

The present disclosure provides a mechanism to support one or morenarrowband TDD frame structure(s) for narrowband communication, asdescribed below with reference to FIGS. 5A-5D.

FIG. 4 is a diagram illustrating a narrowband TDD frame structure 400that may be used for narrowband communication in accordance with certainaspects of the disclosure. In aspect, the narrowband TDD frame structure400 used for narrowband communication may be determined from the groupof narrowband TDD frame structures (e.g., configuration 0-configurationn) listed in table 410. In certain aspects, a base station may determinethe narrowband TDD frame structure based on higher layer signaling(e.g., RRC messaging) received from the network. In certain otheraspects, the base station may determine the narrowband TDD framestructure based on channel conditions.

In one aspect, the narrowband TDD frame structure 400 may include a 10ms radio frame split into two half frames, each 5 ms long. Thehalf-frames may be further split into five subframes, each 1 ms long.The narrowband TDD frame structure 400 may be any one of the narrowbandconfigurations listed in table 410.

Switching periodicity refers to the time a UE uses to switch betweenmonitoring a downlink subframe (e.g., for a downlink transmission from abase station) and sending a transmission using an uplink subframe, orvice versa. Depending on the determined narrowband TDD frame structure400, the switching periodicity may be 5 ms, 10 ms, or more than 10 ms(e.g., 20 ms). For narrowband TDD frame structures 412 with a 5 msswitching periodicity, a special subframe (SSF) may be located in bothhalf frames of the narrowband TDD frame structure 400. For narrowbandTDD frame structures 414 with a 10 ms switching periodicity, a specialsubframe may be located in the first half frame but not in the secondhalf frame. For narrowband TDD frame structures 416 with more than a 10ms switching periodicity, no special subframes may be needed since morethan an entire frame can be used to perform the switch. In thenarrowband TDD frame structures 412, 414 that include a special subframe(e.g., configurations 0, 1, 2, 3, 4, 5, and 6), subframes 0 and 5 aswell as the Downlink Pilot Time Slot (DwPTS) in the special subframe maybe reserved for downlink transmissions. Additionally and/oralternatively, in the narrowband TDD frame structures 412, 414 thatinclude a special subframe, the Uplink Pilot Time Slot (UpPTS) in thespecial subframe and the subframe immediately following the specialsubframe may be reserved for an uplink transmission.

When operating in in-band mode and/or guard-band mode, the narrowbandTDD frame structure 400 may reuse certain LTE TDD frame structures(e.g., configurations 0, 1, 2, 3, 4, 5, 6). When operating in standalonemode, some subframes in the narrowband TDD frame structure 400 may bemarked as flexible subframes (e.g., configurations m and n) and may beused as either a downlink subframe or an uplink subframe by a UEdepending on the current grant received from the base station.

In certain aspects, a subset of the narrowband TDD configurations listedin table 410 in FIG. 4 may be used to support narrowband communications.For example, configuration 0 may not be suitable for narrowbandcommunications because configuration 0 only has two downlink subframes,and hence, may not support repeated transmissions to the UE. In certainaspects, narrowband communications that use a narrowband TDD framestructure may only be supported in in-band mode and/or guard-band mode(e.g., but not standalone mode). In certain other aspects, narrowbandcommunications that use a narrowband TDD frame structure may supportin-band mode, guard-band mode, and standalone mode.

Multiple narrowband downlink carriers and multiple narrowband uplinkcarriers may be used to enhance narrowband communication between a basestation and a UE. Among the carriers, a narrowband anchor carrier may beused to provide synchronization, system information, paging, data, andcontrol for multi-carrier enabled. UEs. Overhead narrowband systeminformation may be reduced when a narrowband anchor carrier is used. Forinstance, synchronization and paging for a certain cell may not be notprovided on all narrowband carriers. Narrowband carriers that do notprovide synchronization and/or paging may be referred to as narrowbandnon-anchor carriers. Coordination between base stations for selectinganchor carriers that mitigate interference, and coordination betweenbase stations for non-anchor carrier transmit power control may providefurther network performance advantages.

Information indicating the determined narrowband TDD frame structure 400may be transmitted from the base station to the UE using narrowband PSS(NPSS), narrowband SSS (NSSS), narrowband PBCH (NPBCH) and/or SIB (e.g.,using the narrowband anchor carrier).

For in-band mode and guard-band mode, the narrowband anchor carrier usedfor narrowband communication (e.g., using a narrowband TDD framestructure) may be located in RB pairs for downlink transmissions fromthe base station to the UE. In certain aspects, the UE may monitor oneRB at any given time. In one example, the SIB and/or NPBCH may arrive atthe UE in a first RB of the RB pair, and the NPSS and/or NSSS may arriveat the UE in a second RB in the pair. In another example, the SIB mayarrive at the UE in a first RB of the RB pair and the NPSS, NSSS, and/orthe NPBCH may arrive at the UE in a second RB in the pair. A location ofone RB may be determined (e.g., implicitly derived) by the UE based onthe location of the other RB in the pair, or based on a location of adifferent RB in a different RB pair.

In addition, the UE may send uplink transmissions using RB pairs. Incertain aspects, the UE may determine which of the RB pairs to use foruplink transmissions based on signaling (e.g., higher layer signaling)received from the base station. In certain other aspects, the UE maydetermine which RB pairs to use for uplink transmissions based on thetype of uplink channels being transmitted (e.g., PRACH and ACK/NACK usesone RB and PUSCH uses the other RB). In certain other aspects, the UEmay determine which RB pairs to use for uplink transmission based on thecoverage level and/or channel conditions.

FIG. 5A is a diagram illustrating a data flow 500 that may be used fornarrowband communications in accordance with certain aspects of thedisclosure. For example, the data flow 500 may be performed by a basestation 504 and/or UE 506. Base station 504 may correspond to, e.g.,base station 102, 180, eNB 310, apparatus 1102/1102′, 1302/1302′,1502/1502′, 1702/1702′, 1902/1902′, 2302/2302′. UE 506 may correspondto, e.g., UE 104, 350, 1150, 1350, 1550, 1750, 1950, 2350. In addition,the base station 504 and the UE 506 may be configured to communicateusing narrowband communications 509 (e.g., NB-IoT and/or eMTC). Forexample, the UE 506 may be an NB-IoT device and/or an eMTC device. InFIG. 5A, optional operations are indicated with dashed lines.

Referring to FIG. 5A, base station 504 may operate 501 in standalonemode, and the base station may use a standalone mode bandwidth (e.g.,1.08 MHz or 180 kHz) for the narrowband communications 509 that isdifferent than a bandwidth available for LTE communications (e.g., 1.4MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz, 100 MHz, etc.).

In certain aspects, base station 504 may determine 503 a narrowband TDDframe structure for narrowband communications 509. In one aspect, thenarrowband TDD frame structure may be a TDD frame structure that isdifferent than an LTE TDD frame structure available for LTEcommunications. For example, the base station 504 may determine thenarrowband TDD frame structure is either configuration m or n from table410 in FIG. 4. Configuration m or n from table 410 may not be availablefor LTE communications.

In certain other aspects, the base station 504 may determine 503 anarrowband TDD frame structure from a subset of the configurations fromtable 410 in FIG. 4. For example, base station 504 may determine 503 thenarrowband TDD frame structure from configurations 1, 2, 3, 4, 5, m,and/or n. In certain aspects, configurations 0 and 6 may not be used forthe narrowband TDD frame structure since configurations 0 and 6 have asmall number of downlink subframes compared to the other configurations,and hence, may not support repeated transmissions.

When base station 504 repeats a downlink transmission, the base station504 may choose a narrowband TDD frame structure with at least a minimumnumber of downlink subframes (e.g., at least three downlink subframes)so that the downlink transmission may be repeated in each of thedownlink subframes.

In certain other aspects, base station 504 may determine 503 anarrowband TDD frame structure for the narrowband communications 509based on a switching periodicity used by the base station 504 and/or theUE 506 to switch from transmitting on downlink subframes to monitoringuplink subframes, or vice versa. For example, when the switchingperiodicity used by base station 504 and/or UE 506 is longer than aswitching periodicity in LTE TDD frame structures (e.g., configurations0, 1, 2, 3, 4, 5, and 6), base station 504 may select eitherconfiguration m or n because the switching periodicity of configurationm and n are both greater than 10 ms (e.g., 20 ms).

In a first example, the narrowband TDD frame structure determined by thebase station 504 may be configuration n (e.g., see FIG. 4).Configuration n may include a plurality of flexible subframes that mayeach be dynamically configured as a downlink subframe, uplink subframe,or special subframe by the base station 504. Configuration n may providethe base station 504 with the flexibility to have a downlinktransmission or an uplink transmission (e.g., based on channelconditions) in order to increase the chance of the UE 506 properlydecoding a transmission.

In a second example, the narrowband TDD frame structure determined bythe base station 504 may be one of configuration 3, 4, 5, m, or n (e.g.,seen in FIG. 4). The narrowband TDD frame structure associated withconfigurations 3, 4, 5, m, and n each include at least three downlinksubframes (e.g., the flexible subframes in configuration n may bedynamically configured by base station 504 such that the TDD framestructure has three or more downlink subframes). Using a narrowband TDDframe structure with at least three downlink subframes may enable basestation 504 to send the NPSS, NSSS, and NPBCH in different subframes ofthe same radio frame, as described below with reference to FIGS. 5B-5D.In certain aspects, repetition of the NPSS, NSSS, and NPBCH may beimplemented by repeating the NPSS, NSSS, and NPBCH over multiple symbolsin the same subframe. If configuration 4, 5, m, or n (e.g.,configurations with four downlink subframes or that are configurablewith four downlink subframes) is determined for use as the narrowbandTDD frame structure, an SIB 507 may also be transmitted in a subframedifferent than the subframe used to transmit the NSSS 505. For example,assuming base station 504 determines the narrowband TDD frame structureis configuration 5, base station 504 may transmit the NSSS 505 insubframe 5 and transmit the SIB 507 in subframe 7.

In certain aspects, base station 504 may use at least three consecutivedownlink subframes to repeat a downlink transmission. If a narrowbandTDD frame structure is used for the repeated downlink transmission thathas less than three contiguous downlink subframes (e.g., configurations0, 1, and 2 in FIG. 4), the duration over which the repeatedtransmission is sent may be increased as compared to a duration of thesame number of repetitions transmitted using a narrowband TDD framestructure with at least three contiguous downlink subframes. Forexample, the duration may be increased due to the presence of uplinksubframes and/or unused flexible subframes located between downlinksubframes used to repeat the transmission. The likelihood that channelconditions may change over the repeated transmission using a narrowbandTDD frame structure with less than three contiguous downlink subframesmay therefore be increased as compared to a repeated transmission usinga narrowband TDD frame structure with at least three contiguous downlinksubframes. Hence, the UE 506 may be less likely to combine the repeatedtransmission received in a narrowband TDD frame structure with less thanthree contiguous downlink subframes.

FIGS. 5B-5D illustrate a data flow 510 that may be used for narrowbandcommunications in accordance with certain aspects of the disclosure. Forexample, the data flow 500 may be performed by a base station 504 and/orUE 506 (e.g., the base station 504 and the UE 506 in FIG. 5A). Basestation 504 may correspond to base station 102, 180, eNB 310, apparatus1102/1102′, 1302/1302′, 1502/1502′, 1702/1702′, 1902/1902′, 2302/2302′.UE 506 may correspond to UE 104, 350, 1150, 1350, 1550, 1750, 1950,2350. In addition, the base station 504 and the UE 506 may be configuredto communicate using narrowband communications 509 (e.g., NB-IoT and/oreMTC). For example, the UE 506 may be an NB-IoT device and/or an eMTCdevice. In FIGS. 5B-5D, optional operations are indicated with dashedlines.

Referring to FIG. 5B, base station 504 may operate 513 in in-band mode,guard band mode, or standalone mode. In certain aspects, base station504 may determine 515 a narrowband TDD frame structure for thenarrowband communications 509 (see FIG. 5D) from a group of narrowbandTDD frame structures (e.g., the configurations listed in table 410 inFIG. 4). In one aspect, each narrowband TDD frame structure in the groupof narrowband TDD frame structures may include at least one commondownlink subframe, as described below.

NPSS

In certain aspects, base station 504 may determine 517 a common subframefrom a plurality of common subframes to use in transmitting an NPSS 521.For example, when the determine narrowband TDD frame structure is one ofconfigurations 0, 1, 2, 3, 4, 5, 6, or m, the NPSS 521 may be sent onone of subframe 0 or subframe 5 because subframes 0 and 5 are the commondownlink subframes in each of configurations 0, 1, 2, 3, 4, 5, 6, and m.In another example, when the determined narrowband TDD frame structureis determined from a subset of the configurations listed in table 410(e.g., one of configurations 1, 2, 3, 4, 5, or 6), the NPSS 521 may besent on one of subframe 0, subframe 5, or subframe 9 because subframes0, 5, and 9 are common downlink subframes in each of configurations 1,2, 3, 4, 5, and 6. Additionally and/or alternatively, the subframe usedto transmit the NPSS 521 may be a function of the determined narrowbandTDD frame structure. In one example, the function may be that the firstdownlink subframe in the narrowband TDD frame structure may be used totransmit the NPSS 521. In certain aspects, a periodicity (e.g., onceevery 20 ms) associated with a NPSS transmitted using the narrowband TDDframe structure may shorter or be longer as compared to a NPSStransmitted using a narrowband FDD frame structure (e.g., once every 10ms). Reduced periodicity of NPSS transmissions (e.g., more frequenttransmission of NPSS) may be useful if the NPSS carrier and NPBCHcarrier are different, and the NPSS carrier cannot be power boosted asmuch as in FDD, for example. In such a scenario, the UE 506 may use moreNPSS averaging to achieve increase coverage. Increased periodicity ofNPSS transmissions (e.g., less frequent transmission of NPSS) may beuseful so that transmissions of NPBCH, NPSS, NSSS, SIB, etc. can beaccommodated in the same carrier.

In certain other aspects, base station 504 may determine 519 a sequence(e.g., a Zadoff Chu sequence) associated with the NPSS 521. In certainother aspects, the NPSS sequences 521 may be associated with at leastone of the TDD mode or the determined narrowband TDD frame structure. Incertain other aspects, the NPSS 521 may have the same set of sequencesas an NPSS transmitted using a narrowband FDD frame structure. An FDDNPSS sequence may comprise a Zadoff Chu sequence of length 11 with rootindex 5, and the same sequence may be flipped in sign on some symbols toprovide better timing properties. In certain other aspects, the NPSS 521may have a different set of sequences than an NPSS transmitted using anarrowband FDD frame structure. In certain other aspects, the NPSS 521may have a different Zadoff Chu sequence for initialization than an NPSStransmitted in a FDD frame structure. In certain other aspects, the NPSS521 transmitted using the determined narrowband TDD frame structure mayhave a different cover code than an NPSS transmitted using a narrowbandFDD frame structure. While the use of different NPSS sequences fornarrowband TDD may add complexity to the processing at the UE, if a UEis aware that certain bands only support TDD or FDD, the UE 506 maylimit the NPSS search to only one corresponding sequence in order toreduce such complexity.

NSSS

Referring to FIG. 5C, base station 504 may transmit an NSSS 529 usingthe determined narrowband TDD frame structure. In one aspect, theperiodicity of the NSSS 529 transmitted using the narrowband TDD framestructure may be the same as compared to the periodicity of an NSSStransmitted using a narrowband FDD frame structure, which is transmittedin subframe 9 of every other radio frame.

Alternatively, the periodicity of the NSSS 529 transmitted using thenarrowband TDD frame structure may be increased as compared to theperiodicity of an NSSS transmitted using a narrowband FDD framestructure, which is transmitted in subframe 9 of every other radioframe. Hence, the periodicity of the NSSS 529 transmitted using thenarrowband TDD frame structure may be greater than two radio frames.Increasing the periodicity of transmitting the NSSS 529 may bebeneficial if separate carriers for NPSS 521/NSSS 529 and NPBCH/SIBbecause the NSSS subframe may not be usable otherwise. Also since NRSmay not be present on the NSSS carrier, additional NSSS measurements maybe needed.

In certain aspects, the NSSS 529 may be transmitted using a different RB(e.g., carrier) than the RB used to transmit the NPSS 521. In scenarioswhen the periodicity of the NPSS 521 is reduced (e.g., NPSS 521 is nottransmitted in every radio frame) or increased (e.g., NPSS 521 istransmitted in every radio frame or more than once every radio frame),the NSSS 529 may be transmitted in radio frames that do not include theNPSS 521. Increasing the periodicity associated with might make sense ifwe have separate carriers for PSS/SSS and PBCH/SIB as the SSS subframemay not be usable otherwise. Also since NRS are not present anymore onthat carrier may need more SSS for measurements.

Additionally and/or alternatively, the NSSS 529 and the NPSS 521 may bemultiplexed such that one of the NSSS 529 or the NPSS 521 is transmittedin an even numbered subframe and the other one of the NSSS 529 or theNPSS 521 is transmitted in an odd numbered subframe.

In certain aspects, base station 504 may determine 517 a common subframefrom a plurality of common subframes described above to transmit NSSS529. For example, when the narrowband TDD frame structure is determinedfrom one of configurations 0, 1, 2, 3, 4, 5, 6, and m, the NSSS 529 maybe sent on one of subframe 0 or subframe 5 because subframes 0 and 5 arethe common downlink subframes in each configuration in the group. Inanother example, when the narrowband TDD frame structure is determinedfrom one of configurations 1, 2, 3, 4, 5, and 6, the NSSS 529 may besent on one of subframe 0, subframe 5, or subframe 9 because subframes0, 5, and 9 are the common downlink subframes in each of configurations1, 2, 3, 4, 5, and 6. In one example, NSSS may be sent on a specialsubframe, which may cause a length of the NSSS to be different for anarrowband TDD configuration than for a narrowband FDD configuration.

In one aspect, base station 504 may determine 523 at least one of theperiodicity of the NSSS 529, a location in time of the NSSS 529, or alocation in frequency of the NSSS 529 as a function of the determinednarrowband TDD frame structure.

In certain aspects, UE 506 may be able to differentiate betweennarrowband FDD frame structure and a narrowband TDD frame structurewhile performing an NSSS search 527. For example, when a narrowband FDDframe structure is used, the base station 504 may transmit the NPSS 521in subframe 5 in odd numbered radio frames and the NSSS 529 in subframe9 in even numbered radio frames. In certain other aspects, base station504 may transmit the NPSS 521 in subframe 0 in odd numbered radio framesand the NSSS 529 in subframe 5 in even numbered radio frames. In certainother aspects, base station 504 may transmit the NPSS 521 in subframe 5in even numbered radio frames and the NSSS 529 in subframe 0 in oddnumbered radio frames. Based on the subframe number and even/odd radioframes used to transmit the NPSS 521 and the NSSS 529, the UE 506 may beable to determine (e.g., implicitly without signaling from the basestation 504) if a narrowband FDD frame structure or a narrowband TDDframe structure is used by the base station 504. Additionally and/oralternatively, the UE 506 may be able to determine 531 a cellidentification (ID) and timing information based on the NSSS 529. Forexample, the UE 506 may use the NSSS to determine a cell ID and a radioframe boundary (e.g., 20 ms frame boundary).

Referring to FIG. 5C, base station 504 may determine 525 a predetermineddistance (e.g., subframe distance and/or radio frame boundary) betweenthe NPSS 521 and the NSSS 529, and use the predetermined distance toconvey information to UE 506. For example, the predetermined distancemay be configured to convey information associated with at least one ofthe TDD mode (e.g., in-band mode, guard band mode, and/or standalonemode) used by base station 504, an FDD mode, the determined narrowbandTDD frame structure, a bandwidth associated with the TDD mode, or atheta f or Of mapping associated with the narrowband TDD frame structureand used to indicate the NSSS 529 sequence. For narrowbandcommunications using a narrowband FDD frame structure, the θ_(f) mappingmay be used to indicate the NSSS sequence. For example, θ_(f) may bedefined as θ_(f)=33/132(n_(f)/2)mod 4. In narrowband communicationsusing a narrowband TDD frame structure, the Of mapping may be the sameas that used for a narrowband FDD frame structure expect that the valueof n_(f) is different. The distance between the NPSS 521 and the NSSS529 may be used to convey the value of n_(f) that the UE 506 may use todetermine the NSSS sequence using θ_(f) mapping.

NPBCH

Referring to FIG. 5D, when the base station 504 operates in in-bandmode, base station 504 may determine 533 in which of the commonsubframes described above to transmit the NPBCH 535. In one aspect, thebase station 504 may transmit the NPBCH 535 in a different narrowbandcarrier than the narrowband carrier used to transmit the NPSS 521 and/orthe NSSS 529.

For example, when the narrowband TDD frame structure is determined fromone of configurations 0, 1, 2, 3, 4, 5, 6, and m, the NPBCH 535 may besent on one of subframe 0 or subframe 5 because subframes 0 and 5 arecommon downlink subframes in each configuration in the group. In anotherexample, when the narrowband TDD frame structure is determined from oneof configurations 1, 2, 3, 4, 5, and 6, the NPBCH 535 may be sent on oneof subframe 0, subframe 5, or subframe 9 because subframes 0, 5, and 9are common downlink subframes in each configuration in the group.Alternatively, base station 504 may transmit the NPBCH 535 in radioframes that do not include NSSS 529 (e.g., in order to accommodate theNSSS 529).

In certain aspects, the periodicity of NPBCH transmissions using thenarrowband TDD frame structure may be reduced as compared to theperiodicity of NPBCH transmissions using a narrowband FDD framestructure.

In certain scenarios, UE 506 may not have knowledge prior to the NPBCHdecoding process if base station 504 is using a narrowband FDD framestructure or a narrowband TDD frame structure. In such scenarios, UE 506may hypothesize whether base station 504 is using a narrowband FDD framestructure or a narrowband TDD frame structure during the NPBCH decodingprocess. To avoid scenarios in which the UE 506 hypothesizes the type offrame structure, base station 504 may include information in the NPBCH535 to indicate to UE 506 that the narrowband TDD frame structure isbeing used. For example, base station 504 may include cyclic redundancycheck (CRC) masking in the NPBCH 535 to indicate the narrowband TDDframe structure is being used. Additionally and/or alternatively, theCRC masking in the NPBCH 535 may indicate to UE 506 which configuration(e.g., see table 410 in FIG. 4) the narrowband TDD frame structure uses.Further, including the CRC masking may keep legacy UEs (e.g., UEs notconfigured for narrowband communications using a TDD frame structure)from attempting to decode the NPBCH 535.

In certain other aspects, the periodicity of the NPBCH 535, the locationin time of the NPBCH 535, or a location in frequency of the NPBCH 535transmitted by base station 504 may be related to the determinednarrowband TDD frame structure.

Additionally, the NPBCH 535 may include a first bit that may indicate toUE 506 if a narrowband TDD frame structure is being used, a second bitthat may indicate to UE 506 if a narrowband FDD frame structure beingused, information indicating a RB location or subframe locationassociated with an SIB 537 transmitted by base station 504, orinformation used for decoding the SIB 537. In another aspect, the NPBCH535 may include a single bit that may indicate to the UE 506 if anarrowband TDD frame structure or a narrowband FDD frame structure isbeing used.

SIB

In certain aspects, base station 504 may transmit SIB 537 (e.g., SIB-1)using the same RB and/or a different RB as the RB used to transmit oneor more of the NPSS 521, the NSSS 529, and/or the NPBCH 535. Thebandwidth used for the narrowband communications 509, deployment type(e.g., in-band mode, guard band mode, standalone mode), and/or frequencylocation associated with the NPBCH 535 may be used to by UE 506 to inferwhich RB is used to carry the SIB 537.

In certain aspects, base station 504 may transmit the SIB 537 using oneof the common subframes described above. For example, when thenarrowband TDD frame structure is one of configurations 0, 1, 2, 3, 4,5, 6, and m, the SIB 537 may be sent on one of subframe 0 or subframe 5because subframes 0 and 5 are common downlink subframes in eachconfiguration in the group. In another example, when the narrowband TDDframe structure is determined from one of configurations 1, 2, 3, 4, 5,and 6, the SIB 537 may be sent on one of subframe 0, subframe 5, orsubframe 9 because subframes 0, 5, and 9 are common downlink subframesin each of configuration 1, 2, 3, 4, 5, and 6. Alternatively, basestation 504 may transmit the SIB 537 in a downlink subframe that is afunction of the determined narrowband TDD frame structure (e.g.,transmit SIB 537 in the first downlink subframe).

NRS

In certain aspects, base station 504 may transmit a narrowband referencesignal (NRS) 541 using the narrowband TDD frame structure determined forthe narrowband communications 509. For example, base station 504 maytransmit the NRS using a subframe that is also used to transmit the SIB537 and/or NPBCH 535. Additionally, the NRS 541 may be transmitted usinga different narrowband carrier than the narrowband carrier used totransmit the NPSS 521 and/or the NSSS 529.

In certain other aspects, base station 504 may transmit the NRS 541using one of the common subframes described above. For example, when thenarrowband TDD frame structure is determined from one of configurations0, 1, 2, 3, 4, 5, 6, and m, the NRS 541 may be sent on one of subframe 0or subframe 5 because subframes 0 and 5 are common downlink subframes ineach configuration in the group. Further, the NRS 541 may be sent onsubframe 1 or subframe 6 because subframes 1 and 6 are special subframes(e.g., that include downlink resources) or downlink subframes in each ofconfiguration 0, 1, 2, 3, 4, 5, 6, and m. In another example, when thenarrowband TDD frame structure is determined from one of configurations1, 2, 3, 4, 5, and 6, the NRS 541 may be sent on one of subframe 0,subframe 5, or subframe 9 because subframes 0, 5, and 9 are commondownlink subframes in each configuration in the group. Alternatively,base station 504 may transmit the NRS 541 in a downlink subframe that isnot a function of the determined narrowband TDD frame structure. Forexample, a NPBCH 535 transmitted (e.g., broadcast signaling) by basestation 504 may be used to indicate the downlink subframes that includethe NRS 541 to UE 506 when the downlink subframe used to transmit theNRS 541 is not a function of the determined narrowband TDD framestructure. In certain aspects, a bitmap 539 may be included in NPBCH535.

In one aspect, the NRS 541 may be transmitted in the DwPTS portion(e.g., see FIG. 4) of a special subframe and in downlink subframes inthe determined narrowband TDD frame structure. In one aspect, the samesymbols in the DwPTS portion of the special subframe and the downlinksubframes may be used to transmit the NRS 541. When the NRS 541 istransmitted in the DwPTS of the special subframe, the UpPTS portion ofthe special subframe may be punctured.

In certain aspects, a density of the NRS 541 transmitted using thenarrowband TDD frame structure may be greater than an NRS densitytransmitted using a narrowband FDD frame structure. In other words, theNRS 541 occupancy (e.g., density) in the time-frequency grid may belarger in a narrowband TDD frame structure than in a narrowband FDDframe structure. Hence, a higher pilot density in the narrowband TDDframe structure may be used because, unlike the narrowband FDD framestructure, the narrowband TDD frame structure may have a reduced numberof downlink subframes with which to average the channel variationsand/or noise variations. In certain other aspects, the NRS 541 may betransmitted in a same subframe that base station 504 uses to transmit aCRS.

FIG. 6 is a flowchart 600 of a method of wireless communication. Themethod may be performed by a base station (e.g., the base station 102,180, 504, eNB 310, the apparatus 1102/1102′, 1302/1302′, 1502/1502′,1702/1702′, 1902/1902′, 2302/2302′). In FIG. 6, optional operations areindicated with dashed lines.

At 602, the base station may determine a bandwidth for narrowbandcommunications. In one aspect, the bandwidth for the narrowbandcommunications may be include at least one flexible subframe that may beconfigured as an uplink subframe, a downlink subframe, or a specialsubframe depending on what is being transmitted by either the basestation and/or the UE. For example, referring to FIG. 5A, base station504 may operate 501 in standalone mode, and the bandwidth associatedwith standalone mode (e.g., the bandwidth the base station 504determines to use for the narrowband communications 509) may bedifferent than a bandwidth available for LTE communications.

At 604, the base station may determine a narrowband TDD frame structurefor the narrowband communications. In certain configurations, thenarrowband TDD frame structure may include two or more contiguousdownlink subframes, or one or more flexible subframes that can beconfigured as either a downlink subframe or an uplink subframe. Incertain other configurations, when a first duration is used by the UE toswitch between monitoring a downlink subframe to sending a transmissionusing an uplink subframe, a special subframe may be located in both halfframes of the narrowband TDD frame structure. In certain otherconfigurations, when a second duration that is longer than the firstduration is used by the UE to switch between monitoring the downlinksubframe to sending the transmission using the uplink subframe, aspecial subframe may be located in a first half frame of the narrowbandTDD frame structure but not the second half frame of the narrowband TDDframe structure. In certain other configurations, when a third durationthat is longer than the second duration is used by the UE to switchbetween monitoring the downlink subframe to sending the transmissionusing the uplink subframe, no special subframes are present in thenarrowband TDD frame structure. In certain other configurations, thenarrowband TDD frame structure for the narrowband communications may bedifferent than another TDD frame structure actively being used in anoverlapping frequency region by a different RAT. For example, referringto FIG. 5A, base station 504 may determine 503 a narrowband TDD framestructure for narrowband communications 509. In one aspect, thenarrowband TDD frame structure determined by the base station 504 mayinclude a TDD frame structure that is different than an LTE TDD framestructure available for LTE communications. For example, the basestation 504 may determine the narrowband TDD frame structure is eitherconfiguration m or n from table 410 in FIG. 4. When base station 504repeats a downlink transmission, the base station 504 may choose anarrowband TDD frame structure with at least a minimum number ofdownlink subframes (e.g., at least three downlink subframes) so that thedownlink transmission may be repeated in each of the downlink subframes.Using a narrowband TDD frame structure with at least three downlinksubframes may enable base station 504 to send the NPSS, NSSS, and NPBCHin different subframes of the same radio frame, as described above withreference to FIGS. 5B-5D. In certain aspects, repetition of the NPSS,NSSS, and NPBCH may be implemented by repeating the NPSS, NSSS, andNPBCH over multiple symbols in the same subframe. Additionally and/oralternatively, base station 504 may determine 503 a narrowband TDD framestructure for the narrowband communications 509 based on a switchingperiodicity used by the base station 504 and/or the UE 506 to switchfrom transmitting on downlink subframes to monitoring uplink subframes,or vice versa. For example, when the switching periodicity used by basestation 504 and/or UE 506 is longer than a switching periodicity in LTETDD frame structures (e.g., configurations 0, 1, 2, 3, 4, 5, and 6),base station 504 may select either configuration m or n because theswitching periodicity of configuration m and n are both greater than 10ms (e.g., 20 ms). In certain configurations, the narrowband TDD framestructure (e.g., configuration morn illustrated in FIG. 4) may includetwo or more contiguous downlink subframes, or one or more flexiblesubframes that can be configured as either a downlink subframe or anuplink subframe. For example, the narrowband TDD frame structure mayinclude at least three contiguous downlink subframes (e.g.,configurations 3, 4, 5, and m illustrated in FIG. 4). In certain otherconfigurations, when a first duration is used by the UE 506 to switchbetween monitoring a downlink subframe to sending a transmission usingan uplink subframe, a special subframe may be located in both halfframes of the narrowband TDD frame structure (e.g., configurations 0, 1,2, and 6 illustrated in FIG. 4). In certain other configurations, when asecond duration that is longer than the first duration is used by the UE506 to switch between monitoring the downlink subframe to sending thetransmission using the uplink subframe, a special subframe may belocated in a first half frame of the narrowband TDD frame structure butnot the second half frame of the narrowband TDD frame structure (e.g.,configurations 3, 4, and 5 illustrated in FIG. 4). In certain otherconfigurations, when a third duration that is longer than the secondduration is used by the UE 506 to switch between monitoring the downlinksubframe to sending the transmission using the uplink subframe, nospecial subframes are present in the narrowband TDD frame structure(e.g., configuration m illustrated in FIG. 4). In certain otherconfigurations, the narrowband TDD frame structure for the narrowbandcommunications (e.g., configurations m or n illustrated in FIG. 4) maybe different than another TDD frame structure (e.g., configurations 0,1, 2, 3, 4, 5, and 6 illustrated in FIG. 4) actively being used in anoverlapping frequency region by a different RAT.

At 606, the base station may transmit a SIB in a first subframe of thenarrowband TDD frame structure. For example, referring to FIG. 5A, ifone of configuration 4, 5, m, or n (e.g., configurations with fourdownlink subframes or configurations that are configurable with fourdownlink subframes) is determined for use as the narrowband TDD framestructure, an SIB 507 may also be transmitted in a subframe differentthan the subframe used to transmit the NSSS 505, as discussed above withrespect to FIGS. 5B-5D. For example, assuming base station 504determines the narrowband TDD frame structure includes configuration 5,base station 504 may transmit the NSSS 505 in subframe 5 and transmitthe SIB 507 in subframe 7, or vice versa.

At 608, the base station may transmit a SSS in a second subframe of thenarrowband TDD frame structure. In one aspect, the second subframe maybe different than the first subframe. For example, referring to FIG. 5A,if one of configurations 4, 5, m, or n (e.g., configurations with fourdownlink subframes or configurations that are configurable with fourdownlink subframes) is determined for use as the narrowband TDD framestructure, an SIB 507 may also be transmitted in a subframe differentthan the subframe used to transmit the NSSS 505, as discussed above withreference to FIGS. 5B-5D. For example, assuming base station 504determines the narrowband TDD frame structure includes configuration 5,base station 504 may transmit the NSSS 505 in subframe 5 and transmitthe SIB 507 in subframe 7, or vice versa.

At 610, the base station may communicate with a UE using the narrowbandTDD frame structure determined for the narrowband communications. Forexample, referring to FIG. 5A, the base station 504 and the UE 506 maybe configured to communicate using narrowband communications 509 (e.g.,NB-IoT and/or eMTC).

FIG. 7 is a flowchart 700 of a method of wireless communication. Themethod may be performed by a base station (e.g., the base station 102,180, 504, eNB 310, the apparatus 1102/1102′, 1302/1302′, 1502/1502′,1702/1702′, 1902/1902′, 2302/2302′). In FIG. 7, optional operations areindicated with dashed lines.

At 702, the base station may determine a TDD mode for narrowbandcommunications. For example, referring to FIGS. 5B-5D, base station 504may operate 513 in in-band mode, guard band mode, or standalone mode.

At 704, the base station may determine a TDD frame structure for thenarrowband communications from a group of narrowband TDD framestructures. In one aspect, at least one common subframe in eachnarrowband TDD frame structure in the group of narrowband TDD framestructures may be configured as a downlink subframe. In another aspect,a first periodicity associated with the PSS using the narrowband TDDframe structure may be increased as compared to a second periodicityassociated with a transmission of a second PSS using a narrowband FDDframe structure. For example, referring to FIGS. 5B-5D, base station 504may determine 515 a narrowband TDD frame structure for the narrowbandcommunications 509 from a group of narrowband TDD frame structures(e.g., the configurations listed in table 410 in FIG. 4). In one aspect,each narrowband TDD frame structure in the group of narrowband TDD framestructures may include at least one common downlink subframe. Basestation 504 may determine 515 which of the common subframes to use intransmitting an NPSS 521. For example, when the narrowband TDD framestructure is determined from one of configurations 0, 1, 2, 3, 4, 5, 6,and m, the NPSS 521 may be sent on one of subframe 0 or subframe 5because subframes 0 and 5 are the common downlink subframes in each ofconfigurations 0, 1, 2, 3, 4, 5, 6, and m. In another example, when thenarrowband TDD frame structure is determined from one of configurations1, 2, 3, 4, 5, and 6, the NPSS 521 may be sent on one of subframe 0,subframe 5, or subframe 9 because subframes 0, 5, and 9 are commondownlink subframes in each configuration in the group. Additionallyand/or alternatively, the subframe used to transmit the NPSS 521 may bea function of the determined narrowband TDD frame structure. In oneexample, the function may be that the first downlink subframe in thenarrowband TDD frame structure may be used to transmit the NPSS 521. Incertain aspects, a periodicity (e.g., once every 20 ms) associated withNPSS transmissions in the narrowband TDD frame structure may be reducedas compared to NPSS transmission in a narrowband FDD frame structure.

At 706, the base station may determine one of the plurality of commonsubframes for use in transmitting the PSS. In one aspect, the one of theplurality of common subframes may be determined as a function of thenarrowband TDD frame structure selected for the narrowbandcommunications. For example, referring to FIGS. 5B-5D, base station 504may determine 515 which of the common subframes to use in transmittingan NPSS 521. In certain aspects, when the narrowband TDD frame structureis determined from one of configurations 0, 1, 2, 3, 4, 5, 6, and m, theNPSS 521 may be sent on one of subframe 0 or subframe 5 becausesubframes 0 and 5 are the common downlink subframes in eachconfiguration in the group. In certain other aspects, when thenarrowband TDD frame structure is determined from one of configurations1, 2, 3, 4, 5, and 6, the NPSS 521 may be sent on one of subframe 0,subframe 5, or subframe 9 because subframes 0, 5, and 9 are commondownlink subframes in each configuration in the group. Additionallyand/or alternatively, the subframe used to transmit the NPSS 521 may bea function of the determined narrowband TDD frame structure. In oneexample, the function may be that the first downlink subframe in thenarrowband TDD frame structure may be used to transmit the NPSS 521. Incertain other aspects, a periodicity (e.g., once every 20 ms) associatedwith NPSS transmissions in the narrowband TDD frame structure may bereduced as compared to NPSS transmission in a narrowband FDD framestructure.

At 708, the base station may transmit a PSS using the at least onecommon subframe in the narrowband TDD frame structure determined for thenarrowband communications. In one aspect, a first periodicity associatedwith the transmitting the PSS using the narrowband TDD frame structuremay be reduced or increased as compared to a second periodicityassociated with transmission of a second PSS using a narrowband FDDframe structure. For example, referring to FIGS. 5B-5D, base station 504may determine 515 which of the common subframes to use in transmittingan NPSS 521. For example, when the narrowband TDD frame structure isdetermined from one of configurations 0, 1, 2, 3, 4, 5, 6, and m, theNPSS 521 may be sent on one of subframe 0 or subframe 5 becausesubframes 0 and 5 are the common downlink subframes in eachconfiguration in the group. In another example, when the narrowband TDDframe structure is determined from one of configurations 1, 2, 3, 4, 5,and 6, the NPSS 521 may be sent on one of subframe 0, subframe 5, orsubframe 9 because subframes 0, 5, and 9 are common downlink subframesin each configuration in the group. Additionally and/or alternatively,the subframe used to transmit the NPSS 521 may be a function of thedetermined narrowband TDD frame structure. In one example, the functionmay be that the first downlink subframe in the narrowband TDD framestructure may be used to transmit the NPSS 521. In certain aspects, aperiodicity (e.g., once every 20 ms) associated with NPSS transmissionsin the narrowband TDD frame structure may be reduced as compared to NPSStransmission in a narrowband FDD frame structure. In certain aspects, aperiodicity (e.g., once every 20 ms) associated with NPSS transmissionsin the narrowband TDD frame structure may be reduced as compared to NPSStransmission in a narrowband FDD frame structure.

FIG. 8 is a flowchart 800 of a method of wireless communication. Themethod may be performed by a base station (e.g., the base station 102,180, 504, eNB 310, the apparatus 1102/1102′, 1302/1302′, 1502/1502′,1702/1702′, 1902/1902′, 2302/2302′).

At 802, the base station may determine a TDD mode for narrowbandcommunications. For example, referring to FIGS. 5B-5D, base station 504in may operate 513 in in-band mode, guard band mode, or standalone mode.

At 804, the base station may determine a narrowband TDD frame structurefor the narrowband communications from a group of narrowband TDD framestructures. For example, referring to FIGS. 5B-5D, base station 504 maydetermine 515 a narrowband TDD frame structure for the narrowbandcommunications 509 from a group of narrowband TDD frame structures(e.g., the configurations listed in table 410 in FIG. 4). In one aspect,each narrowband TDD frame structure in the group of narrowband TDD framestructures may include at least one common downlink subframe. Basestation 504 may determine 515 which of the common subframes to use intransmitting an NPSS 521. For example, when the narrowband TDD framestructure is determined from one of configurations 0, 1, 2, 3, 4, 5, 6,and m, the NPSS 521 may be sent on one of subframe 0 or subframe 5because subframes 0 and 5 are the common downlink subframes in eachconfiguration in the group. In another example, when the narrowband TDDframe structure is determined from one of configurations 1, 2, 3, 4, 5,and 6, the NPSS 521 may be sent on one of subframe 0, subframe 5, orsubframe 9 because subframes 0, 5, and 9 are common downlink subframesin each configuration in the group. Additionally and/or alternatively,the subframe used to transmit the NPSS 521 may be a function of thedetermined narrowband TDD frame structure. In one example, the functionmay be that the first downlink subframe in the narrowband TDD framestructure may be used to transmit the NPSS 521.

At 806, the base station may transmit a PSS using the narrowband TDDframe structure selected for the narrowband communications. In oneaspect, a set of PSS sequences may be associated with at least one ofthe TDD mode or the determined narrowband TDD frame structure. Inanother aspect, the set of PSS sequences transmitted using thenarrowband TDD frame structure may be the same as a second set of PSSsequences transmitted using a narrowband FDD frame structure. In afurther aspect, the set of PSS sequences transmitted using thenarrowband TDD frame structure may be different than a second set of PSSsequences transmitted using a narrowband FDD frame structure. In certainother aspects, the set of PSS sequences transmitted using the narrowbandTDD frame structure may have a different Zadoff Chu sequence forinitialization than the second set of PSS sequences transmitted using anarrowband FDD frame structure. In certain other aspects, the set of PSSsequences transmitted using the narrowband TDD frame structure may havea different cover code than the second set of PSS sequences transmittedusing a narrowband FDD frame structure. For example, referring to FIGS.5B-5D, base station 504 may determine 519 a sequence associated with theNPSS 521. In one aspect, the sequence of the NPSS 521 may be associatedwith at least one of the TDD mode or the determine narrowband TDD framestructure. In certain aspects, the NPSS 521 transmitted using thedetermine narrowband TDD frame structure may have the same sequence asan NPSS transmitted using a narrowband FDD frame structure. In certainother aspects, the NPSS 521 transmitted using the determined narrowbandTDD frame structure may have a different sequence than an NPSStransmitted using a narrowband FDD frame structure. In certain otheraspects, the NPSS 521 transmitted using the determined narrowband TDDframe structure may have a different Zadoff Chu sequence forinitialization than an NPSS transmitted in a FDD frame structure. Incertain other aspects, the NPSS 521 transmitted using the determinednarrowband TDD frame structure may have a different cover code than anNPSS transmitted using a narrowband FDD frame structure.

FIG. 9 is a flowchart 900 of a method of wireless communication. Themethod may be performed by a base station (e.g., the base station 102,180, 504, eNB 310, the apparatus 1102/1102′, 1302/1302′, 1502/1502′,1702/1702′, 1902/1902′, 2302/2302′). In FIG. 9, optional operations arewith dashed lines.

At 902, the base station may determine a narrowband communication framestructure comprising a FDD mode or a TDD mode and a particular TDD framestructure for narrowband communications from a group of narrowband TDDframe structures. In one aspect, least one common subframe in eachnarrowband TDD frame structure in the group of narrowband TDD framestructures may be configured as a downlink subframe. In another aspect,the SSS may be transmitted using the at least one common subframe in thenarrowband TDD frame structure determined for the narrowbandcommunications. In a further aspect, the group of narrowband TDD framestructures may include a subset of all narrowband TDD frame structuresavailable for narrowband communications. For example, referring to FIGS.5B-5D, base station 504 may determine 515 a narrowband TDD framestructure for the narrowband communications 509 from a group ofnarrowband TDD frame structures (e.g., the configurations listed intable 410 in FIG. 4). When the narrowband TDD frame structure isdetermined from one of configurations 0, 1, 2, 3, 4, 5, 6, and m, theNSSS 529 may be sent on one of subframe 0 or subframe 5 becausesubframes 0 and 5 are the common downlink subframes in eachconfiguration in the group. In another example, when the narrowband TDDframe structure is determined from one of configurations 1, 2, 3, 4, 5,and 6, the NSSS 529 may be sent on one of subframe 0, subframe 5, orsubframe 9 because subframes 0, 5, and 9 are the common downlinksubframes in each configuration in the group.

At 904, the base station may determine an SSS sequence and apredetermined distance between transmitting the PSS and SSS. In oneaspect, at least one of the SSS sequence or the predetermined distancemay be configured to convey information associated with the narrowbandcommunications to a UE. In another aspect, the information may includeat least one of the TDD mode, the FDD mode, the narrowband TDD framestructure determined for narrowband communications, a bandwidthassociated with the TDD mode, or a frequency offset of a first carrierused to transmit a physical broadcast channel (PBCH) or systeminformation block (SIB) relative to a second carrier used to transmitone or more of the SSS or the PSS. For example, referring to FIGS.5B-5D, base station 504 may determine a predetermined distance (e.g.,subframe distance) between the NPSS 521 and the NSSS 529, and use thepredetermined distance to convey information to UE 506. For example, thepredetermined distance may be configured to convey informationassociated with at least one of the TDD mode (e.g., in-band mode, guardband mode, and/or standalone mode) used by base station 504, an FDDmode, the determined narrowband TDD frame structure, a bandwidthassociated with the TDD mode, or a θ_(f) mapping associated with thenarrowband TDD frame structure and used to indicate the NSSS 529sequence. For narrowband communications using a narrowband FDD framestructure, the θ_(f) mapping used to indicate the NSSS sequence may bedefined as θ_(f)=33/132(n_(f)/2)mod 4. In narrowband communicationsusing a narrowband TDD frame structure, the θ_(f) mapping may be thesame as that used for a narrowband FDD frame structure expect that thevalue of n_(f) is different. The distance between the NPSS 521 and theNSSS 529 may be used to convey the value of n_(f) that the UE 506 mayuse to determine the NSSS sequence using θf mapping.

At 906, the base station may determine a periodicity, subframe number,and transmission sequence associated with a SSS based at least in parton the narrowband TDD frame structure. For example, referring to FIGS.5B-5D, the NSSS 529 may be transmitted using a different RB (e.g.,carrier) than the RB used to transmit the NPSS 521. In configurationswhen the periodicity of the NPSS 521 is reduced (e.g., NPSS 521 is nottransmitted in every radio frame), the NSSS 529 may be transmitted inradio frames that do not include the NPSS 521. In one aspect, the NSSS529 may be transmitted in the same subframe number that is used totransmit the NPSS 521 but in radio frames that do not include NPSS 521.For example, assuming that NPSS 521 is transmitted in subframe 5 in evennumbered radio frames, NSSS 529 may be transmitted in subframe 5 in oddnumbered radio frames. Alternatively, base station 504 may transmit theNPSS 521 in subframe 0 in odd numbered radio frames and the NSSS 529 insubframe 5 in even numbered radio frames. In another configuration, basestation 504 may transmit the NPSS 521 in subframe 5 in even numberedradio frames and the NSSS 529 in subframe 0 in odd numbered radioframes.

At 908, the base station may transmit a PSS using the narrowband TDDframe structure determined for the narrowband communications. In anaspect, the PSS may be transmitted on a different narrowband carrierthan the SSS. In another aspect, the PSS may be transmitted using aparticular subframe. In a further aspect, the PSS may not be transmittedin every frame. In a further aspect, the SSS may be transmitted usingthe particular subframe in at least one frame in which the PSS is nottransmitted.

In still another aspect, the PSS may be transmitted using a particularsubframe. In still a further aspect, the SSS may be transmitted using asubframe other than the particular subframe. For example, referring toFIGS. 5B-5D, the NSSS 529 may be transmitted using a different RB (e.g.,carrier) than the RB used to transmit the NPSS 521. In configurationswhen the periodicity of the NPSS 521 is reduced (e.g., NPSS 521 is nottransmitted in every radio frame), the NSSS 529 may be transmitted inradio frames that do not include the NPSS 521. In one aspect, the NSSS529 may be transmitted in the same subframe number that is used totransmit the NPSS 521 but in radio frames that do not include NPSS 521.For example, assuming that NPSS 521 is transmitted in subframe 5 in evennumbered radio frames, NSSS 529 may be transmitted in subframe 5 in oddnumbered radio frames. Alternatively, base station 504 may transmit theNPSS 521 in subframe 0 in odd numbered radio frames and the NSSS 529 insubframe 5 in even numbered radio frames. In another configuration, basestation 504 may transmit the NPSS 521 in subframe 5 in even numberedradio frames and the NSSS 529 in subframe 0 in odd numbered radioframes.

At 910, the base station may transmit an SSS using the narrowband TDDframe structure determined for the narrowband communications. In anaspect, the SSS may be transmitted using a same subframe in at mostevery other frame. In another aspect, a periodicity associated withtransmitting the SSS using the narrowband TDD frame structure may beincreased or reduced as compared to a periodicity associated withtransmission of a second SSS using a narrowband FDD frame structure. Ina further aspect, at least one of the periodicity associated withtransmitting the SSS, a location in time associated with transmittingthe SSS, or a location in frequency associated with transmitting the SSSis related to the narrowband TDD frame structure determined fornarrowband communications. For example, referring to FIGS. 5B-5D, basestation 504 may transmit an NSSS 529 using the determined narrowband TDDframe structure. In one aspect, the NSSS 529 may be transmitted in thesame subframe in every other radio frame. In other words, theperiodicity of the NSSS 529 transmitted using the narrowband TDD framestructure may be reduced as compared to the periodicity of an NSSStransmitted using a narrowband FDD frame structure. Base station 504 maydetermine 523 at least one of the periodicity of the NSSS 529, alocation in time of the NSSS 529, or a location in frequency of the NSSS529 as a function of the determined narrowband TDD frame structure.

FIG. 10 is a flowchart 1000 of a method of wireless communication. Themethod may be performed by a base station (e.g., the base station 102,180, 504, eNB 310, the apparatus 1102/1102′, 1302/1302′, 1502/1502′,1702/1702′, 1902/1902′, 2302/2302′).

At 1002, the base station may determine a narrowband communication framestructure comprising a FDD frame structure or a TDD frame structure anda narrowband TDD frame structure configuration for narrowbandcommunications from a group of narrowband TDD frame structuresconfigurations. For example, referring to FIGS. 5B-5D, base station 504may determine 515 to either use a FDD frame structure or a TDD framestructure that includes a narrowband TDD frame structure configurationfor the narrowband communications 509 from a group of narrowband TDDframe structures (e.g., the configurations listed in table 410 in FIG.4).

At 1004, the base station may determine one or more narrowband carriersand subframes within the one or more narrowband carriers to transmit atleast one of a BCH or a SIB1 based on the narrowband communication framestructure or the TDD frame structure configuration. For example,referring to FIGS. 5B-5D, base station 504 may determine one or morenarrowband carriers and subframes within the one or more narrowbandcarriers to transmit the SIB (e.g., SIB1) and/or the BCH. The basestation 504 may transmit SIB 537 using the same RB (e.g., carrier) or adifferent RB as the RB used to transmit one or more of the NPSS 521, theNSSS 529, and/or the NPBCH 535. The bandwidth used for the narrowbandcommunications 509, deployment type (e.g., in-band mode, guard bandmode, standalone mode), and/or frequency location associated with theNPBCH 535 may be used to by UE 506 to infer which RB is used to transmitthe SIB 537 to UE 506.

At 1006, the base station may transmit a PSS, an SSS, and at least oneof a BCH or an SIB1 using the narrowband TDD frame structure determinedfor the narrowband communications. In one aspect, a carrier used fortransmitting the BCH and/or the SIB may be different than a carrier usedto transmit one or more of the PSS or the SSS. In another aspect, anarrowband carrier used for transmitting the BCH may be different than anarrowband carrier used to transmit one or more of the PSS or the SSS.In another aspect, the BCH may be transmitted using one or moresubframes in every radio frame. In certain other aspects, the SSS may betransmitted using a particular subframe in every other frame. In certainother aspects, the BCH may be transmitted using the particular subframein each frame in which the SSS is not transmitted. In certain otheraspects, a periodicity associated with the transmitting the BCH may beused to indicate which of the FDD frame structure or the TDD framestructure is being used for the narrowband communications. In certainother aspects, at least one of a periodicity associated with thetransmitting the BCH, a location in time associated with thetransmitting the BCH, or a location in frequency associated with thetransmitting the BCH may be related to one or more of the narrowband TDDframe structure determined for narrowband communications, the secondcarrier containing the PSS or the SSS, or information sent on the PSS orthe SSS. In certain other aspects, the first carrier used to transmitthe BCH may be located at a fixed frequency offset with respect to thesecond carrier used to transmit the one or more of the PSS or the SSS.In certain other aspects, the BCH includes information that indicates atleast one of the narrowband TDD frame structure configuration determinedfor the narrowband communications, whether a narrowband communicationsuse uses the FDD frame structure or the TDD frame structure, or acarrier location or subframe location associated with the SIB1. Incertain other aspects, the information may be included in the BCH by atleast one of including additional bits in a payload, by using differentCRC masks based on the additional bits, or by using different scramblingcodes based on the additional bits. In certain other aspects, the firstcarrier may be used to transmit both the BCH and the SIB1 when the firstcarrier is different than the second carrier used to transmit the PSSand SSS. In certain other aspects, the SIB1 may be transmitted using adifferent carrier than the first carrier used to transmit the BCH. Incertain other aspects, at least one of a narrowband carrier locationrelative to the PSS carrier location or a subframe used to transmit theSIB1 may be associated with the narrowband frame structure determinedfor the narrowband communications. For example, referring to FIGS.5B-5D, base station 504 may transmit a NPBCH 535 using the determinednarrowband TDD frame structure. In one aspect, the base station 504 maytransmit the NPBCH 535 in a different RB than the RB used to transmitthe NPSS 521 and/or the NSSS 529. UE 506 may not know before the NPBCHdecoding process if base station 504 is using a narrowband FDD framestructure or a narrowband TDD frame structure. In such scenarios, UE 506may hypothesize whether base station 504 is using a narrowband FDD framestructure or a narrowband TDD frame structure during the NPBCH decodingprocess. To avoid scenarios in which the UE 506 hypothesizes a type offrame structure, base station 504 may include information in the NPBCH535 to indicate to UE 506 that the narrowband TDD frame structure isbeing used. For example, base station 504 may include CRC masking in theNPBCH 535 to indicate the narrowband TDD frame structure is being used.In addition, including the CRC masking may keep legacy UEs (e.g., UEsnot configured for narrowband communications using a TDD framestructure) from attempting to decode the NPBCH 535. In certain aspects,the periodicity of the NPBCH 535, the location in time of the NPBCH 535,or a location in frequency of the NPBCH 535 transmitted by base station504 may be related to the determined narrowband TDD frame structure.Additionally, the NPBCH 535 may include a first bit that may indicate toUE 506 if a narrowband TDD frame structure being used, a second bit thatmay indicate to UE 506 if a narrowband FDD frame structure being used,information indicating a RB location or subframe location associatedwith an SIB 537 transmitted by base station 504, or information used fordecoding the SIB 537.

FIG. 11 is a conceptual data flow diagram 1100 illustrating the dataflow between different means/components in an exemplary apparatus 1102.The apparatus may be a base station (e.g., the base station 102, 180,310, 504, the apparatus 1102′, 1302/1302′, 1502/1502′, 1702/1702′,1902/1902′, 2302/2302′) in narrowband communication (e.g., NB-IoTcommunication or eMTC) with UE 1150 (e.g., UE 104, 350, 506, 1350, 1550,1750, 1950, 2350). The apparatus may include a reception component 1104,a determination component 1106, and a transmission component 1108.

The determination component 1106 may be configured to determine abandwidth for narrowband communications. In one aspect, the bandwidthfor the narrowband communications may be different than a bandwidthavailable for LTE communications. The determination component 1106 maybe configured to determine a narrowband TDD frame structure for thenarrowband communications. In an aspect, the narrowband TDD framestructure may be different than an LTE TDD frame structure available forLTE communications. In another aspect, a switching periodicity fromdownlink subframes to uplink subframes in the narrowband TDD framestructure may be longer than a switching periodicity in LTE TDD framestructures. In a further aspect, the narrowband TDD frame structure hasat least three contiguous downlink subframes. The determinationcomponent 1106 may be configured to send a signal 1101 includinginformation associated with the bandwidth for narrowband communicationsand/or the narrowband TDD frame structure for the narrowbandcommunications to the transmission component 1108.

The transmission component 1108 may be configured to transmit a SIB 1103in a first subframe of the narrowband TDD frame structure to the UE1150. The transmission component 1108 may be configured to transmit aSSS 1103 in a second subframe of the narrowband TDD frame structure. Inone aspect, the second subframe may be different than the firstsubframe. The transmission component 1108 may be configured to transmitinformation associated with one or more of information 1103 associatedwith the bandwidth for narrowband communications and/or information 1103the narrowband TDD frame structure for the narrowband communications toUE 1150.

The reception component 1104 and/or the transmission component 1108 maybe configured to communicate 1103, 1105 with the UE 1150 using thenarrowband TDD frame structure determined for narrowband communications.For example, the reception component 1104 may be configured to receivenarrowband uplink transmissions 1105 from the UE 1150. The transmissioncomponent 1108 may be configured to transmit one or more narrowbanddownlink transmissions 1103 to the UE 1150.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowchart of FIG. 6. Assuch, each block in the aforementioned flowchart of FIG. 6 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 12 is a diagram 1200 illustrating an example of a hardwareimplementation for an apparatus 1102′ employing a processing system1214. The processing system 1214 may be implemented with a busarchitecture, represented generally by the bus 1224. The bus 1224 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1214 and the overalldesign constraints. The bus 1224 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1204, the components 1104, 1106, 1108, and thecomputer-readable medium/memory 1206. The bus 1224 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1214 may be coupled to a transceiver 1210. Thetransceiver 1210 is coupled to one or more antennas 1220. Thetransceiver 1210 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1210 receives asignal from the one or more antennas 1220, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1214, specifically the reception component 1104. Inaddition, the transceiver 1210 receives information from the processingsystem 1214, specifically the transmission component 1108, and based onthe received information, generates a signal to be applied to the one ormore antennas 1220. The processing system 1214 includes a processor 1204coupled to a computer-readable medium/memory 1206. The processor 1204 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1206. The software, whenexecuted by the processor 1204, causes the processing system 1214 toperform the various functions described above for any particularapparatus. The computer-readable medium/memory 1206 may also be used forstoring data that is manipulated by the processor 1204 when executingsoftware. The processing system 1214 further includes at least one ofthe components 1104, 1106, 1108. The components may be softwarecomponents running in the processor 1204, resident/stored in thecomputer readable medium/memory 1206, one or more hardware componentscoupled to the processor 1204, or some combination thereof. Theprocessing system 1214 may be a component of the eNB 310 and may includethe memory 376 and/or at least one of the TX processor 316, the RXprocessor 370, and the controller/processor 375.

In certain aspects, the apparatus 1102/1102′ for wireless communicationmay include means for determining a bandwidth for narrowbandcommunications. In one aspect, the bandwidth for the narrowbandcommunications may be different than a bandwidth available for LTEcommunications. In certain other aspects, the apparatus 1102/1102′ forwireless communication may include means for determining a narrowbandTDD frame structure for the narrowband communications. In an aspect, thenarrowband TDD frame structure may be different than an LTE TDD framestructure available for LTE communications. In another aspect, aswitching periodicity from downlink subframes to uplink subframes in thenarrowband TDD frame structure may be longer than a switchingperiodicity in LTE TDD frame structures. In a further aspect, thenarrowband TDD frame structure has at least three contiguous downlinksubframes. In certain other aspects, the apparatus 1102/1102′ forwireless communication may include means for transmitting an SIB in afirst subframe of the narrowband TDD frame structure. In certain otheraspects, the apparatus 1102/1102′ for wireless communication may includemeans for transmitting an SSS in a second subframe of the narrowband TDDframe structure. In one aspect, the second subframe may be differentthan the first subframe. In certain other aspects, the apparatus1102/1102′ for wireless communication may include means forcommunicating with a UE using the narrowband TDD frame structuredetermined for the narrowband communications. The aforementioned meansmay be one or more of the aforementioned components of the apparatus1102 and/or the processing system 1214 of the apparatus 1102′ configuredto perform the functions recited by the aforementioned means. Asdescribed above, the processing system 1214 may include the TX Processor316, the RX Processor 370, and the controller/processor 375. As such, inone configuration, the aforementioned means may be the TX Processor 316,the RX Processor 370, and the controller/processor 375 configured toperform the functions recited by the aforementioned means.

FIG. 13 is a conceptual data flow diagram 1300 illustrating the dataflow between different means/components in an exemplary apparatus 1302.The apparatus may be a base station (e.g., the base station 102, 180,310, 504, the apparatus 1102/1102′, 1302′, 1502/1502′, 1702/1702′,1902/1902′, 2302/2302′) in narrowband communication (e.g., NB-IoTcommunication or eMTC) with UE 1350 (e.g., UE 104, 350, 506, 1150, 1550,1750, 1950, 2350). The apparatus may include a reception component 1304,a determination component 1306, and a transmission component 1308.

The determination component 1306 may be configured to determine a TDDmode for narrowband communications. The determination component 1306 maybe configured to determine a TDD frame structure for the narrowbandcommunications from a group of narrowband TDD frame structures. In oneaspect, at least one common subframe in each narrowband TDD framestructure in the group of narrowband TDD frame structures may beconfigured as a downlink subframe. In another aspect, a firstperiodicity associated with the PSS using the narrowband TDD framestructure may be increased as compared to a second periodicityassociated with transmission of a second PSS using a narrowband FDDframe structure. The determination component 1306 may be configured todetermine one of a plurality of common subframes for use in transmittingthe PSS. In one aspect, the one of the plurality of common subframes maybe determined as a function of the narrowband TDD frame structureselected for the narrowband communications. The determination component1306 may be configured to send a signal 1301 that includes informationassociated with one or more of the TDD mode for narrowbandcommunications, TDD frame structure for narrowband communications,and/or the one of the plurality of common subframes to the transmissioncomponent 1308.

The transmission component 1308 may be configured to transmitinformation 1303 associated with one or more of the TDD mode fornarrowband communications, TDD frame structure for narrowbandcommunications, and/or the one of the plurality of common subframes tothe UE 1350. The transmission component 1308 may be configured totransmit a PSS 1303 (e.g., NPSS) using the at least one common subframein the narrowband TDD frame structure determined for the narrowbandcommunications. In one aspect, a first periodicity associated with thetransmitting the PSS 1303 using the narrowband TDD frame structure maybe increased as compared to a second periodicity associated withtransmission of a second PSS 1303 using a narrowband FDD framestructure.

The reception component 1304 and/or the transmission component 1308 maybe configured to communicate 1303, 1305 with the UE 1350 using thenarrowband TDD frame structure determined for narrowband communications.For example, the reception component 1304 may be configured to receivenarrowband uplink transmissions 1305 from the UE 1350. The transmissioncomponent 1308 may be configured to transmit one or more narrowbanddownlink transmissions 1303 to the UE 1350.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowchart of FIG. 7. Assuch, each block in the aforementioned flowchart of FIG. 7 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 14 is a diagram 1400 illustrating an example of a hardwareimplementation for an apparatus 1302′ employing a processing system1414. The processing system 1414 may be implemented with a busarchitecture, represented generally by the bus 1424. The bus 1424 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1414 and the overalldesign constraints. The bus 1424 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1404, the components 1304, 1306, 1308, and thecomputer-readable medium/memory 1406. The bus 1424 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1414 may be coupled to a transceiver 1410. Thetransceiver 1410 is coupled to one or more antennas 1420. Thetransceiver 1410 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1410 receives asignal from the one or more antennas 1420, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1414, specifically the reception component 1304. Inaddition, the transceiver 1410 receives information from the processingsystem 1414, specifically the transmission component 1308, and based onthe received information, generates a signal to be applied to the one ormore antennas 1420. The processing system 1414 includes a processor 1404coupled to a computer-readable medium/memory 1406. The processor 1404 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1406. The software, whenexecuted by the processor 1404, causes the processing system 1414 toperform the various functions described above for any particularapparatus. The computer-readable medium/memory 1406 may also be used forstoring data that is manipulated by the processor 1404 when executingsoftware. The processing system 1414 further includes at least one ofthe components 1304, 1306, 1308. The components may be softwarecomponents running in the processor 1404, resident/stored in thecomputer readable medium/memory 1406, one or more hardware componentscoupled to the processor 1404, or some combination thereof. Theprocessing system 1414 may be a component of the base station 310 andmay include the memory 376 and/or at least one of the TX processor 316,the RX processor 370, and the controller/processor 375.

In certain aspects, the apparatus 1302/1302′ for wireless communicationmay include means for determining a TDD mode for narrowbandcommunications. In certain other aspects, the apparatus 1302/1302′ forwireless communication may include means for determining a TDD framestructure for the narrowband communications from a group of narrowbandTDD frame structures. In one aspect, at least one common subframe ineach narrowband TDD frame structure in the group of narrowband TDD framestructures may be configured as a downlink subframe. In another aspect,a first periodicity associated with the PSS using the narrowband TDDframe structure may be increased as compared to a second periodicityassociated with transmission of a second PSS using a narrowband FDDframe structure. In certain other aspects, the apparatus 1302/1302′ forwireless communication may include means for determining one of theplurality of common subframes for use in transmitting the PSS. In oneconfiguration, the one of the plurality of common subframes may bedetermined as a function of the narrowband TDD frame structure selectedfor the narrowband communications. In certain other aspects, theapparatus 1302/1302′ for wireless communication may include means fortransmitting a PSS using the at least one common subframe in thenarrowband TDD frame structure determined for the narrowbandcommunications. In one aspect, a first periodicity associated with thetransmitting the PSS using the narrowband TDD frame structure may beincreased as compared to a second periodicity associated withtransmission of a second PSS using a narrowband FDD frame structure. Theaforementioned means may be one or more of the aforementioned componentsof the apparatus 1302 and/or the processing system 1414 of the apparatus1302′ configured to perform the functions recited by the aforementionedmeans. As described above, the processing system 1414 may include the TXProcessor 316, the RX Processor 370, and the controller/processor 375.As such, in one configuration, the aforementioned means may be the TXProcessor 316, the RX Processor 370, and the controller/processor 375configured to perform the functions recited by the aforementioned means.

FIG. 15 is a conceptual data flow diagram 1500 illustrating the dataflow between different means/components in an exemplary apparatus 1502.The apparatus may be a base station (e.g., the base station 102, 180,310, 504, the apparatus 1102/1102′, 1302/1302′, 1502′, 1702/1702′,1902/1902′, 2302/2302′) in narrowband communication (e.g., NB-IoTcommunication or eMTC) with UE 1550 (e.g., UE 104, 350, 506, 1150, 1350,1750, 1950, 2350). The apparatus may include a reception component 1504,a determination component 1506, and a transmission component 1508.

The determination component 1506 may be configured to determine a TDDmode for narrowband communications. The determination component 1506 maybe configured to determine a narrowband TDD frame structure for thenarrowband communications from a group of narrowband TDD framestructures. The determination component 1506 may be configured to send asignal 1501 including information associated with one or more of the TDDmode for narrowband communications or the narrowband TDD frame structurefor the narrowband communications.

The transmission component 1508 may be configured to transmit a PSS 1503using the narrowband TDD frame structure selected for the narrowbandcommunications. In one aspect, a sequence of the PSS 1503 may beassociated with at least one of the TDD mode or the determinednarrowband TDD frame structure. In another aspect, the PSS sequencetransmitted using the narrowband TDD frame structure may be the same asa second PSS sequence transmitted using a narrowband FDD framestructure. In a further aspect, the PSS sequence transmitted using thenarrowband TDD frame structure may be different than a second PSSsequence transmitted using a narrowband FDD frame structure. In certainother aspects, the PSS sequence transmitted using the narrowband TDDframe structure may have a different Zadoff Chu sequence forinitialization than the second PSS sequence transmitted using anarrowband FDD frame structure. In certain other aspects, the PSSsequence transmitted using the narrowband TDD frame structure may have adifferent cover code than the second PSS sequence transmitted using anarrowband FDD frame structure. The transmission component 1508 may beconfigured to transmit information 1503 associated with one or more ofthe TDD mode for narrowband communications or the narrowband TDD framestructure for the narrowband communications.

The reception component 1504 and/or the transmission component 1508 maybe configured to communicate 1503, 1505 with the UE 1550 using thenarrowband TDD frame structure determined for narrowband communications.For example, the reception component 1504 may be configured to receivenarrowband uplink transmissions 1505 from the UE 1550. The transmissioncomponent 1508 may be configured to transmit one or more narrowbanddownlink transmissions 1503 to the UE 1550.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowchart of FIG. 8. Assuch, each block in the aforementioned flowchart of FIG. 8 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 16 is a diagram 1600 illustrating an example of a hardwareimplementation for an apparatus 1502′ employing a processing system1614. The processing system 1614 may be implemented with a busarchitecture, represented generally by the bus 1624. The bus 1624 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1614 and the overalldesign constraints. The bus 1624 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1604, the components 1504, 1506, 1508, and thecomputer-readable medium/memory 1606. The bus 1624 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1614 may be coupled to a transceiver 1610. Thetransceiver 1610 is coupled to one or more antennas 1620. Thetransceiver 1610 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1610 receives asignal from the one or more antennas 1620, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1614, specifically the reception component 1504. Inaddition, the transceiver 1610 receives information from the processingsystem 1614, specifically the transmission component 1508, and based onthe received information, generates a signal to be applied to the one ormore antennas 1620. The processing system 1614 includes a processor 1604coupled to a computer-readable medium/memory 1606. The processor 1604 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1606. The software, whenexecuted by the processor 1604, causes the processing system 1614 toperform the various functions described above for any particularapparatus. The computer-readable medium/memory 1606 may also be used forstoring data that is manipulated by the processor 1604 when executingsoftware. The processing system 1614 further includes at least one ofthe components 1504, 1506, 1508. The components may be softwarecomponents running in the processor 1604, resident/stored in thecomputer readable medium/memory 1606, one or more hardware componentscoupled to the processor 1604, or some combination thereof. Theprocessing system 1614 may be a component of the base station 310 andmay include the memory 376 and/or at least one of the TX processor 316,the RX processor 370, and the controller/processor 375.

In certain aspects, the apparatus 1502/1502′ for wireless communicationmay include means for determining a TDD mode for narrowbandcommunications. In certain other aspects, the apparatus 1502/1502′ forwireless communication may include means for determining a narrowbandTDD frame structure for the narrowband communications from a group ofnarrowband TDD frame structures. In certain other aspects, the apparatus1502/1502′ for wireless communication may include means for transmittinga PSS using the narrowband TDD frame structure selected for thenarrowband communications. In one aspect, a sequence of the PSS may beassociated with at least one of the TDD mode or the determinednarrowband TDD frame structure. In another aspect, the PSS sequencetransmitted using the narrowband TDD frame structure may be the same asa second PSS sequence transmitted using a narrowband FDD framestructure. In a further aspect, the PSS sequence transmitted using thenarrowband TDD frame structure may be different than a second PSSsequence transmitted using a narrowband FDD frame structure. In certainother aspects, the PSS sequence transmitted using the narrowband TDDframe structure may have a different Zadoff Chu sequence forinitialization than the second PSS sequence transmitted using anarrowband FDD frame structure. In certain other aspects, the PSSsequence transmitted using the narrowband TDD frame structure may have adifferent cover code than the second PSS sequence transmitted using anarrowband FDD frame structure. The aforementioned means may be one ormore of the aforementioned components of the apparatus 1502 and/or theprocessing system 1614 of the apparatus 1502′ configured to perform thefunctions recited by the aforementioned means. As described above, theprocessing system 1614 may include the TX Processor 316, the RXProcessor 370, and the controller/processor 375. As such, in oneconfiguration, the aforementioned means may be the TX Processor 316, theRX Processor 370, and the controller/processor 375 configured to performthe functions recited by the aforementioned means.

FIG. 17 is a conceptual data flow diagram 1700 illustrating the dataflow between different means/components in an exemplary apparatus 1702.The apparatus may be a base station (e.g., the base station 102, 180,310, 504, the apparatus 1102/1102′, 1302/1302′, 1502/1502′, 1702′,1902/1902′, 2302/2302′) in narrowband communication (e.g., NB-IoTcommunication or eMTC) with UE 1750 (e.g., UE 104, 350, 506, 1150, 1350,1550, 1950, 2350). The apparatus may include a reception component 1704,a determination component 1706, and a transmission component 1708.

The determination component 1706 may be configured to determine anarrowband TDD frame structure for narrowband communications from agroup of narrowband TDD frame structures. In one aspect, least onecommon subframe in each narrowband TDD frame structure in the group ofnarrowband TDD frame structures may be configured as a downlinksubframe. In another aspect, the SSS may be transmitted using the atleast one common subframe in the narrowband TDD frame structuredetermined for the narrowband communications. In a further aspect, thegroup of narrowband TDD frame structures may include a subset of allnarrowband TDD frame structures available for narrowband communications.The determination component 1706 may be configured to determine apredetermined distance between transmitting a PSS and an SSS. In oneaspect, the predetermined distance may be configured to conveyinformation associated with the narrowband communications to a UE. Inanother aspect, the information may include at least one of TDD mode,FDD mode, the narrowband TDD frame structure determined for narrowbandcommunications, or a bandwidth associated with the TDD mode. Thedetermination component 1706 may be configured to send a signal 1701including information associated with at least one of the narrowband TDDframe structure for narrowband communications and/or the predetermineddistance between transmitting the PSS and the SSS to the transmissioncomponent 1708.

The transmission component 1708 may be configured to transmit a PSS 1703using the narrowband TDD frame structure determined for the narrowbandcommunications. In an aspect, the PSS 1703 may be transmitted on adifferent resource block than the SSS. In another aspect, the PSS 1703may be transmitted using a particular subframe. In a further aspect, thePSS 1703 may not be transmitted in every frame. In a further aspect, theSSS 1703 may be transmitted using the particular subframe in at leastone frame in which the PSS 1703 is not transmitted. In still anotheraspect, the PSS 1703 may be transmitted using a particular subframe inevery other frame. In still a further aspect, the SSS 1703 may betransmitted using a subframe other than the particular subframe in eachframe in which the PSS 1703 is not transmitted. The transmissioncomponent 1708 may be configured to transmit an SSS 1703 using thenarrowband TDD frame structure determined for the narrowbandcommunications. In an aspect, the SSS 1703 may be transmitted using asame subframe in at most every other frame. In another aspect, aperiodicity associated with transmitting the SSS 1703 using thenarrowband TDD frame structure may be reduced as compared to aperiodicity associated with transmission of a second SSS 1703 using anarrowband FDD frame structure. In a further aspect, at least one of theperiodicity associated with transmitting the SSS 1703, a location intime associated with transmitting the SSS 1703, or a location infrequency associated with transmitting the SSS 1703 is related to thenarrowband TDD frame structure determined for narrowband communications.

The reception component 1704 and/or the transmission component 1708 maybe configured to communicate 1703, 1705 with the UE 1750 using thenarrowband TDD frame structure determined for narrowband communications.For example, the reception component 1704 may be configured to receivenarrowband uplink transmissions 1705 from the UE 1750. The transmissioncomponent 1708 may be configured to transmit one or more narrowbanddownlink transmissions 1703 to the UE 1750.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowchart of FIG. 9. Assuch, each block in the aforementioned flowchart of FIG. 9 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 18 is a diagram 1800 illustrating an example of a hardwareimplementation for an apparatus 1702′ employing a processing system1814. The processing system 1814 may be implemented with a busarchitecture, represented generally by the bus 1824. The bus 1824 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1814 and the overalldesign constraints. The bus 1824 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1804, the components 1704, 1706, 1708, and thecomputer-readable medium/memory 1806. The bus 1824 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1814 may be coupled to a transceiver 1810. Thetransceiver 1810 is coupled to one or more antennas 1820. Thetransceiver 1810 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1810 receives asignal from the one or more antennas 1820, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1814, specifically the reception component 1704. Inaddition, the transceiver 1810 receives information from the processingsystem 1814, specifically the transmission component 1708, and based onthe received information, generates a signal to be applied to the one ormore antennas 1820. The processing system 1814 includes a processor 1804coupled to a computer-readable medium/memory 1806. The processor 1804 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1806. The software, whenexecuted by the processor 1804, causes the processing system 1814 toperform the various functions described above for any particularapparatus. The computer-readable medium/memory 1806 may also be used forstoring data that is manipulated by the processor 1804 when executingsoftware. The processing system 1814 further includes at least one ofthe components 1704, 1706, 1708. The components may be softwarecomponents running in the processor 1804, resident/stored in thecomputer readable medium/memory 1806, one or more hardware componentscoupled to the processor 1804, or some combination thereof. Theprocessing system 1814 may be a component of the base station 310 andmay include the memory 376 and/or at least one of the TX processor 316,the RX processor 370, and the controller/processor 375.

In certain aspects, the apparatus 1702/1702′ for wireless communicationmay include means for determining a narrowband TDD frame structure fornarrowband communications from a group of narrowband TDD framestructures. In one aspect, least one common subframe in each narrowbandTDD frame structure in the group of narrowband TDD frame structures maybe configured as a downlink subframe. In another aspect, the SSS may betransmitted using the at least one common subframe in the narrowband TDDframe structure determined for the narrowband communications. In afurther aspect, the group of narrowband TDD frame structures may includea subset of all narrowband TDD frame structures available for narrowbandcommunications. In certain other aspects, the apparatus 1702/1702′ forwireless communication may include means for determining a predetermineddistance between transmitting a PSS and an SSS. In one aspect, thepredetermined distance may be configured to convey informationassociated with the narrowband communications to a UE. In anotheraspect, the information may include at least one of TDD mode, FDD mode,the narrowband TDD frame structure determined for narrowbandcommunications, or a bandwidth associated with the TDD mode. In certainother aspects, the apparatus 1702/1702′ for wireless communication mayinclude means for transmitting a PSS using the narrowband TDD framestructure determined for the narrowband communications. In an aspect,the PSS may be transmitted on a different resource block than the SSS.In another aspect, the PSS may be transmitted using a particularsubframe. In a further aspect, the PSS may not be transmitted in everyframe. In a further aspect, the SSS may be transmitted using theparticular subframe in at least one frame in which the PSS is nottransmitted. In still another aspect, the PSS may be transmitted using aparticular subframe in every other frame. In still a further aspect, theSSS may be transmitted using a subframe other than the particularsubframe in each frame in which the PSS is not transmitted. In certainother aspects, the apparatus 1702/1702′ for wireless communication mayinclude means for transmitting an SSS using the narrowband TDD framestructure determined for the narrowband communications. In an aspect,the SSS may be transmitted using a same subframe in at most every otherframe. In another aspect, a periodicity associated with transmitting theSSS using the narrowband TDD frame structure may be reduced as comparedto a periodicity associated with transmission of a second SSS using anarrowband FDD frame structure. In a further aspect, at least one of theperiodicity associated with transmitting the SSS, a location in timeassociated with transmitting the SSS, or a location in frequencyassociated with transmitting the SSS is related to the narrowband TDDframe structure determined for narrowband communications. Theaforementioned means may be one or more of the aforementioned componentsof the apparatus 1702 and/or the processing system 1814 of the apparatus1702′ configured to perform the functions recited by the aforementionedmeans. As described above, the processing system 1814 may include the TXProcessor 316, the RX Processor 370, and the controller/processor 375.As such, in one configuration, the aforementioned means may be the TXProcessor 316, the RX Processor 370, and the controller/processor 375configured to perform the functions recited by the aforementioned means.

FIG. 19 is a conceptual data flow diagram 1900 illustrating the dataflow between different means/components in an exemplary apparatus 1902.The apparatus may be a base station (e.g., the base station 102, 180,310, 504, the apparatus 1102/1102′, 1302/1302′, 1502/1502′, 1702/1702′,1902′, 2302/2302′) in narrowband communication (e.g., NB-IoTcommunication or eMTC) with UE 1950 (e.g., UE 104, 350, 506, 1150, 1350,1550, 1750, 2350). The apparatus may include a reception component 1904,a determination component 1906, and a transmission component 1908.

The determination component 1906 may be configured to determine anarrowband TDD frame structure for narrowband communications from agroup of narrowband TDD frame structures. In one aspect, the narrowbandTDD frame structure including a set of downlink subframes and more thanone special subframe. In certain other configurations, the determinationcomponent 1906 may be configured to determine a set of narrowbandcarriers and a minimum set of subframes on the set of narrowbandcarriers based at least in part on the set of downlink subframes andmore than one special subframe on which a NRS should be transmitted. Thedetermination component 1906 may be configured to send a signal 1901including information associated with the narrowband TDD frame structurefor narrowband communications to the transmission component 1908.

The transmission component 1908 may be configured to transmit a PSS1903, an SSS 1903, and a BCH 1903 using the narrowband TDD framestructure determined for the narrowband communications. In one aspect, aresource block used for transmitting the BCH 1903 may be different thana resource block used to transmit one or more of the PSS 1903 or the SSS1903. In another aspect, the BCH 1903 may be transmitted using one ormore subframes in every radio frame. In a further aspect, the SSS 1903may be transmitted using a particular subframe in every other frame. Instill another aspect, the BCH 1903 may be transmitted using theparticular subframe in each frame in which the SSS is not transmitted.In yet a further aspect, a first periodicity associated with thetransmitting the BCH 1903 using the narrowband TDD frame structure maybe reduced as compared to a second periodicity associated withtransmitting the BCH 1903 using a FDD frame structure. In anotheraspect, a CRC masking may be included in the BCH 1903 to indicate thenarrowband TDD frame structure. In another aspect, at least one of aperiodicity associated with the transmitting the BCH 1903, a location intime associated with the transmitting the BCH, or a location infrequency associated with the transmitting the BCH 1903 may be relatedto the narrowband TDD frame structure determined for narrowbandcommunications. In another aspect, the BCH 1903 may include at least oneof a first bit indicating the narrowband TDD frame structure determinedfor the narrowband communications, a second bit indicating a FDD framestructure determined for the narrowband communications, or informationindicating a resource block location or subframe location associatedwith a SIB 1903. The transmission component 1908 may be configured totransmit a SIB 1903 using the narrowband TDD frame structure determinedfor the narrowband communications. In one aspect, the SIB 1903 may betransmitted using a same resource block as a resource block used totransmit one or more of the PSS 1903, SSS 1903, or BCH 1903. In anotheraspect, the SIB 1903 may be transmitted using a different resource blockas a resource block used to transmit one or more of the PSS 1903, SSS1903, or BCH 1903. In a further aspect, at least one of a resource blockor a subframe used to transmit the SIB 1903 may be associated with thenarrowband TDD frame structure determined for the narrowbandcommunications. The transmission component 1908 may be configured totransmit information indicating additional subframes used to transmitthe NRS 1903. In one aspect, the information may include broadcastsignaling. The transmission component 1908 may be configured to transmita NRS 1903 using the narrowband TDD frame structure determined for thenarrowband communications. In one aspect, the NRS 1903 may betransmitted using a subframe that is also used to transmit the SIB 1903and BCH 1903. In another aspect, the NRS 1903 may be transmitted using aresource block that is different than a resource block used to transmitat least one of the PSS 1903 or the SSS 1903. In another aspect, thesame subframe used to transmit the NRS 1903, SIB 1903, and BCH 1903 maybe not a function of the narrowband TDD frame structure determined forthe narrowband communications. In a further aspect, the same subframeused to transmit the NRS 1903, SIB 1903, and BCH 1903 may be a functionof the narrowband TDD frame structure determined for the narrowbandcommunications. In another aspect, a density of the NRS 1903 transmittedusing the narrowband TDD frame structure may be increased as compared toa density of an NRS 1903 transmitted using a narrowband FDD framestructure. In still another aspect, the NRS 1903 may be transmitted in asymbols and resource elements used to transmit a CRS. In yet a furtheraspect, the NRS 1903 may be transmitted in a downlink portion of aspecial subframe in the narrowband TDD frame structure determined fornarrowband communications. In one aspect, symbols used to transmit theNRS in the downlink portion of the special subframe may be the same assymbols used to transmit the NRS in downlink subframes in the narrowbandTDD frame structure. In another aspect, any NRS symbols present in anuplink portion of the special subframe may be punctured. In a furtheraspect, symbols used to transmit the NRS 1903 in the downlink portion ofthe special subframe may be different than symbols used to transmit theNRS 1903 in downlink subframes in the narrowband TDD frame structure. Incertain aspects, the NRS 1903 may be transmitted on a carrier containinga SIB 1903 or a BCH 1903. In certain other configurations, the minimumset of subframes includes subframes used to transmit the SIB 1903 andthe BCH 1903. In certain other aspects, the minimum set of subframesused to transmit the NRS 1903 may not be a function of the narrowbandTDD frame structure determined for the narrowband communications. Incertain other configurations, the minimum set of subframes may berestricted to subframes which are downlink subframes or specialsubframes in all supported TDD frame structures for the narrowbandcommunications. In certain aspects, the minimum set of subframes used totransmit the NRS 1903 may be a function of the narrowband TDD framestructure determined for the narrowband communications.

The reception component 1904 and/or the transmission component 1908 maybe configured to communicate 1903, 1905 with the UE 1950 using thenarrowband TDD frame structure determined for narrowband communications.For example, the reception component 1904 may be configured to receivenarrowband uplink transmissions 1905 from the UE 1950. The transmissioncomponent 1908 may be configured to transmit one or more narrowbanddownlink transmissions 1903 to the UE 1950.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIGS. 10 and25. As such, each block in the aforementioned flowcharts of FIGS. 10 and25 may be performed by a component and the apparatus may include one ormore of those components. The components may be one or more hardwarecomponents specifically configured to carry out the statedprocesses/algorithm, implemented by a processor configured to performthe stated processes/algorithm, stored within a computer-readable mediumfor implementation by a processor, or some combination thereof.

FIG. 20 is a diagram 2000 illustrating an example of a hardwareimplementation for an apparatus 1902′ employing a processing system2014. The processing system 2014 may be implemented with a busarchitecture, represented generally by the bus 2024. The bus 2024 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 2014 and the overalldesign constraints. The bus 2024 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 2004, the components 1904, 1906, 1908, and thecomputer-readable medium/memory 2006. The bus 2024 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 2014 may be coupled to a transceiver 2010. Thetransceiver 2010 is coupled to one or more antennas 2020. Thetransceiver 2010 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 2010 receives asignal from the one or more antennas 2020, extracts information from thereceived signal, and provides the extracted information to theprocessing system 2014, specifically the reception component 1904. Inaddition, the transceiver 2010 receives information from the processingsystem 2014, specifically the transmission component 1908, and based onthe received information, generates a signal to be applied to the one ormore antennas 2020. The processing system 2014 includes a processor 2004coupled to a computer-readable medium/memory 2006. The processor 2004 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 2006. The software, whenexecuted by the processor 2004, causes the processing system 2014 toperform the various functions described above for any particularapparatus. The computer-readable medium/memory 2006 may also be used forstoring data that is manipulated by the processor 2004 when executingsoftware. The processing system 2014 further includes at least one ofthe components 1904, 1906, 1908. The components may be softwarecomponents running in the processor 2004, resident/stored in thecomputer readable medium/memory 2006, one or more hardware componentscoupled to the processor 2004, or some combination thereof. Theprocessing system 2014 may be a component of the base station 310 andmay include the memory 376 and/or at least one of the TX processor 316,the RX processor 370, and the controller/processor 375.

In certain aspects, the apparatus 1902/1902′ for wireless communicationmay include means for determining a narrowband TDD frame structure fornarrowband communications from a group of narrowband TDD framestructures. In certain configurations, the narrowband TDD framestructure may include a set of downlink subframes and more than onespecial subframe. In certain other aspects, the apparatus 1902/1902′ forwireless communication may include means for determining a set ofnarrowband carriers and a minimum set of subframes on the set ofnarrowband carriers based at least in part on the set of downlinksubframes and more than one special subframe on which a NRS should betransmitted. In certain other aspects, the apparatus 1902/1902′ forwireless communication may include means for transmitting a PSS, an SSS,and a BCH using the narrowband TDD frame structure determined for thenarrowband communications. In one aspect, a resource block used fortransmitting the BCH may be different than a resource block used totransmit one or more of the PSS or the SSS. In another aspect, the BCHmay be transmitted using one or more subframes in every radio frame. Ina further aspect, the SSS may be transmitted using a particular subframein every other frame. In still another aspect, the BCH may betransmitted using the particular subframe in each frame in which the SSSis not transmitted. In yet a further aspect, a first periodicityassociated with the transmitting the BCH using the narrowband TDD framestructure may be reduced as compared to a second periodicity associatedwith transmitting the BCH using a FDD frame structure. In anotheraspect, a CRC masking may be included in the BCH to indicate thenarrowband TDD frame structure. In another aspect, at least one of aperiodicity associated with the transmitting the BCH, a location in timeassociated with the transmitting the BCH, or a location in frequencyassociated with the transmitting the BCH may be related to thenarrowband TDD frame structure determined for narrowband communications.In another aspect, the BCH may include at least one of a first bitindicating the narrowband TDD frame structure determined for thenarrowband communications, a second bit indicating a FDD frame structuredetermined for the narrowband communications, or information indicatinga resource block location or subframe location associated with a SIB. Incertain other aspects, the apparatus 1902/1902′ for wirelesscommunication may include means for transmitting a system informationblock using the narrowband TDD frame structure determined for thenarrowband communications. In one aspect, the SIB may be transmittedusing a same resource block as a resource block used to transmit one ormore of the PSS, SSS, or BCH. In another aspect, the SIB may betransmitted using a different resource block as a resource block used totransmit one or more of the PSS, SSS, or BCH. In a further aspect, atleast one of a resource block or a subframe used to transmit the SIB maybe associated with the narrowband TDD frame structure determined for thenarrowband communications. In certain other aspects, the apparatus1902/1902′ for wireless communication may include means for transmittinginformation indicating additional subframes used to transmit the NRS. Inone aspect, the information may include broadcast signaling. In certainother aspects, the apparatus 1902/1902′ for wireless communication mayinclude means for transmit a NRS using the narrowband TDD framestructure determined for the narrowband communications. In one aspect,the NRS may be transmitted using a subframe that is also used totransmit the SIB and BCH. In another aspect, the NRS may be transmittedusing a resource block that is different than a resource block used totransmit at least one of the PSS or the SSS. In another aspect, the samesubframe used to transmit the NRS, SIB, and BCH may be not a function ofthe narrowband TDD frame structure determined for the narrowbandcommunications. In a further aspect, the same subframe used to transmitthe NRS, SIB, and BCH may be a function of the narrowband TDD framestructure determined for the narrowband communications. In anotheraspect, a density of the NRS transmitted using the narrowband TDD framestructure may be increased as compared to a density of an NRStransmitted using a narrowband FDD frame structure. In still anotheraspect, the NRS is transmitted in a same subframe used to transmit aCRS. In yet a further aspect, the NRS may be transmitted in a downlinkportion of a special subframe in the narrowband TDD frame structuredetermined for narrowband communications. In one aspect, symbols used totransmit the NRS in the downlink portion of the special subframe may bethe same as symbols used to transmit the NRS in downlink subframes inthe narrowband TDD frame structure. In another aspect, any NRS symbolspresent in the uplink portion of the special subframe may be punctured.In a further aspect, symbols used to transmit the NRS in the downlinkportion of the special subframe may be different than symbols used totransmit the NRS in downlink subframes in the narrowband TDD framestructure. In certain aspects, the NRS may be transmitted on a carriercontaining a SIB or a BCH. In certain other configurations, the minimumset of subframes includes subframes used to transmit the SIB and theBCH. In certain other aspects, the minimum set of subframes used totransmit the NRS may not be a function of the narrowband TDD framestructure determined for the narrowband communications. In certain otherconfigurations, the minimum set of subframes may be restricted tosubframes which are downlink subframes or special subframes in allsupported TDD frame structures for the narrowband communications. Incertain aspects, the minimum set of subframes used to transmit the NRSmay be a function of the narrowband TDD frame structure determined forthe narrowband communications. In certain other aspects, the NRS may betransmitted in symbols and resource elements used to transmit a CRS. Incertain other aspects, symbols used to transmit the NRS may bedetermined based on a number of downlink symbols in a special subframeconfiguration. The aforementioned means may be one or more of theaforementioned components of the apparatus 1902 and/or the processingsystem 2014 of the apparatus 1902′ configured to perform the functionsrecited by the aforementioned means. As described above, the processingsystem 2014 may include the TX Processor 316, the RX Processor 370, andthe controller/processor 375. As such, in one configuration, theaforementioned means may be the TX Processor 316, the RX Processor 370,and the controller/processor 375 configured to perform the functionsrecited by the aforementioned means.

FIG. 21 is a diagram illustrating a data flow 2100 that may be used fornarrowband communications in accordance with certain aspects of thedisclosure. For example, the data flow 2100 may be performed by a basestation 2104 and/or UE 2106. Base station 2104 may correspond to, e.g.,base station 102, 180, 504, eNB 310, apparatus 1102/1102′, 1302/1302′,1502/1502′, 1702/1702′, 1902/1902′, 2302/2302′. UE 2106 may correspondto, e.g., UE 104, 350, 506, 1150, 1350, 1550, 1750, 1950, 2350. Inaddition, the base station 2104 and the UE 2106 may be configured tocommunicate using narrowband communications 2109 (e.g., NB-IoT and/oreMTC). For example, the UE 2106 may be an NB-IoT device and/or an eMTCdevice.

In one aspect, base station 2104 may determine 2101 a narrowband TDDframe structure for narrowband communications. The narrowband TDD framestructure may include one or more of a set of downlink subframes, a setof uplink subframes, a set of special subframes, and/or a set offlexible subframes. For example, base station 2104 may determine 2101that the narrowband TDD frame structure is one of configuration 0, 1, 2,3, 4, 5, 6, l, or o from table 410 in FIG. 4.

In another aspect, base station 2104 may transmit a bitmap 2103associated with the narrowband TDD frame structure to UE 2106. Bitmap2103 may indicate the set of downlink subframes, the set of uplinksubframes, the set of special subframes, and/or the set of flexiblesubframes in the determined narrowband TDD frame structure.

In one aspect, when base station 2104 is operating in in-band mode, asingle bitmap 2103 indicating the set of downlink subframes, the set ofuplink subframes, the set of special subframes, and/or the set offlexible subframes may be transmitted to UE 2106. Alternatively, whenbase station 2104 is operating in standalone mode, a first bitmap 2103that indicates the set of downlink subframes, a second bitmap 2103 thatindicates the set of uplink subframes, a third bitmap 2103 thatindicates the set of special subframes, and/or a fourth bitmap 2103 thatindicates the set of flexible subframes may be separately transmitted toUE 2106.

In certain aspects, a first length of the bitmap 2103 associated withthe determined narrowband TDD frame structure may be longer than asecond length of a different bitmap associated with a narrowband FDDframe structure. For example, a single bitmap of length N (e.g., N=60)be used to indicate or more of downlink subframes and/or uplinksubframes in a narrowband FDD frame structure. In certain aspects, thelength N of bitmap 2103 used to indicate the available downlinksubframes, uplink subframes, special subframes, and/or flexiblesubframes in the narrowband TDD frame structure may be larger (e.g.,N=80) than the bitmap used to indicate the narrowband FDD framestructure. The length of the narrowband TDD frame structure bitmap maybe larger than the narrowband FDD frame structure bitmap because theremay be more types of subframes (e.g., uplink subframes, downlinksubframes, special subframes, and/or flexible subframes) available forallocation using a narrowband TDD frame structure as compared to anarrowband FDD frame structure (e.g., uplink subframes and/or downlinksubframes).

When base station 2104 allocates one or more flexible subframes for theNPDCCH and/or the NPDSCH, UE 2106 may decode NRS and the NPDCCH and/orNPDSCH transmitted on the allocated flexible subframe(s). When basestation 2104 allocates one or more flexible subframes for the NPUCCHand/or the NPUSCH, UE 2106 may use the allocated flexible subframes totransmit the NPUCCH and/or the NPUSCH. When flexible subframes are notallocated for the NPDCCH, NPDSCH, NPUCCH, or NPUSCH, UE 2106 may ignorethe flexible subframes. For example, the UE 2106 may not perform NRSdetection on the flexible subframes when flexible subframes are notallocated for the NPDCCH, NPDSCH, NPUCCH, or NPUSCH.

FIG. 22 is a flowchart 2200 of a method of wireless communication. Themethod may be performed by a base station (e.g., the base station 102,180, 504, 2104, eNB 310, the apparatus 1102/1102′, 1302/1302′,1502/1502′, 1702/1702′, 1902/1902′, 2302/2302′). In FIG. 22, optionaloperations are indicated with dashed lines.

At 2202, the base station may determine a narrowband TDD frame structurefor narrowband communications. In one aspect, the narrowband TDD framestructure may include one or more of a set of downlink subframes, a setof uplink subframes, a set of special subframes, or a set of flexiblesubframes. In one aspect, a flexible subframe may be configurable by thebase station as either a downlink subframe or an uplink subframe. Forexample, referring to FIG. 21, base station 2104 may determine 2101 anarrowband TDD frame structure for narrowband communications thatincludes one or more of a set of downlink subframes, a set of uplinksubframes, a set of special subframes, and/or a set of flexiblesubframes. For example, base station 2104 may determine 2101 that thenarrowband TDD frame structure is one of configuration 0, 1, 2, 3, 4, 5,6, l, or o from table 410 in FIG. 4.

At 2204, the base station may transmit a bitmap associated with thenarrowband TDD frame structure to a UE. In one aspect, the bitmap mayindicate the one or more of the set of downlink subframes, the set ofuplink subframes, the set of special subframes, or the set of flexiblesubframes. In another aspect, a first length of the bitmap associatedwith the narrowband TDD frame structure may be longer than a secondlength of a different bitmap associated with a narrowband FDD framestructure. For example, referring to FIG. 21, base station 2104 maytransmit a bitmap 2103 associated with the narrowband TDD framestructure to UE 2106. Bitmap 2103 may indicate the set of downlinksubframes, the set of uplink subframes, the set of special subframes,and/or the set of flexible subframes in the determined narrowband TDDframe structure.

At 2206, the base station may transmit the bitmap associated with thenarrowband TDD frame structure to the UE by transmitting a single bitmapindicating the one or more of the set of downlink subframes, the set ofuplink subframes, the set of special subframes, or the set of flexiblesubframes. For example, referring to FIG. 21, when base station 2104 isoperating in in-band mode, a single bitmap 2103 indicating the set ofdownlink subframes, the set of uplink subframes, the set of specialsubframes, and/or the set of flexible subframes may be transmitted to UE2106.

At 2208, the base station may transmit the bitmap associated with thenarrowband TDD frame structure to the UE by transmitting firstinformation indicating the set of downlink subframes. For example,referring to FIG. 21, when base station 2104 is operating in standalonemode, a first bitmap 2103 that indicates the set of downlink subframesmay be separately transmitted to UE 2106.

At 2210, the base station may transmit the bitmap associated with thenarrowband TDD frame structure to the UE by transmitting secondinformation indicating the set of uplink subframes. For example,referring to FIG. 21, when base station 2104 is operating in standalonemode, a second bitmap 2103 that indicates the set of uplink subframesmay be separately transmitted to UE 2106.

At 2212, the base station may transmit the bitmap associated with thenarrowband TDD frame structure to the UE by transmitting thirdinformation indicating the set of special subframes. For example,referring to FIG. 21, when base station 2104 is operating in standalonemode, a third bitmap 2103 that indicates the set of special subframesmay be separately transmitted to UE 2106.

At 2214, the base station may transmit the bitmap associated with thenarrowband TDD frame structure to the UE by transmitting fourthinformation indicating the set of flexible subframes. For example,referring to FIG. 21, when base station 2104 is operating in standalonemode, a fourth bitmap 2103 that indicates the set of flexible subframesmay be separately transmitted to UE 2106.

FIG. 23 is a conceptual data flow diagram 2300 illustrating the dataflow between different means/components in an exemplary apparatus 2302.The apparatus may be a base station (e.g., the base station 102, 180,310, 504, 2104, the apparatus 1102/1102′, 1302/1302′, 1502/1502′,1702/1702′, 1902/1902′, 2302′) in narrowband communication (e.g., NB-IoTcommunication or eMTC) with UE 2350 (e.g., UE 104, 350, 506, 1150, 1350,1550, 1950, 2104). The apparatus may include a reception component 2304,a determination component 2306, and a transmission component 2308.

The determination component 2306 may be configured to determine anarrowband TDD frame structure for narrowband communications. In oneaspect, the narrowband TDD frame structure may include one or more of aset of downlink subframes, a set of uplink subframes, a set of specialsubframes, or a set of flexible subframes. In one aspect, a flexiblesubframe may be configurable by the base station as either a downlinksubframe or an uplink subframe. The determination component 2306 maysend a signal 2301 including information associated with the narrowbandTDD frame structure with one or more of a set of downlink subframes, aset of uplink subframes, a set of special subframes, or a set offlexible subframes to the transmission component 2308.

The transmission component 2308 may transmit a bitmap 2303 associatedwith the narrowband TDD frame structure to the UE 2350. In one aspect,the bitmap may indicate the one or more of the set of downlinksubframes, the set of uplink subframes, the set of special subframes, orthe set of flexible subframes. In another aspect, a first length of thebitmap associated with the narrowband TDD frame structure may be longerthan a second length of a different bitmap associated with a narrowbandFDD frame structure. In certain aspects, the transmission component 2308may be configured to transmit the bitmap 2303 associated with thenarrowband TDD frame structure to the UE 2350 by transmitting firstinformation indicating the set of downlink subframes. In certain otheraspects, the transmission component 2308 may be configured to transmitthe bitmap 2303 associated with the narrowband TDD frame structure tothe UE 2350 by transmitting second information indicating the set ofuplink subframes. In certain other aspects, the transmission component2308 may be configured to transmit the bitmap 2303 associated with thenarrowband TDD frame structure to the UE 2350 by transmitting thirdinformation indicating the set of special subframes. In certain otheraspects, the transmission component 2308 may be configured to transmitthe bitmap 2303 associated with the narrowband TDD frame structure tothe UE 2350 by transmitting fourth information indicating the set offlexible subframes.

The reception component 2304 and/or the transmission component 2308 maybe configured to communicate 2303, 2305 with the UE 1750 using thenarrowband TDD frame structure determined for narrowband communications.For example, the reception component 2304 may be configured to receivenarrowband uplink transmissions 2305 from the UE 2350. The transmissioncomponent 2308 may be configured to transmit one or more narrowbanddownlink transmissions 2303 to the UE 2350.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowchart of FIG. 22. Assuch, each block in the aforementioned flowcharts of FIG. 22 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 24 is a diagram 2400 illustrating an example of a hardwareimplementation for an apparatus 2302′ employing a processing system2414. The processing system 2414 may be implemented with a busarchitecture, represented generally by the bus 2424. The bus 2424 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 2414 and the overalldesign constraints. The bus 2424 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 2404, the components 2304, 2306, 2308, and thecomputer-readable medium/memory 2406. The bus 2424 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 2414 may be coupled to a transceiver 2410. Thetransceiver 2410 is coupled to one or more antennas 2420. Thetransceiver 2410 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 2410 receives asignal from the one or more antennas 2420, extracts information from thereceived signal, and provides the extracted information to theprocessing system 2414, specifically the reception component 2304. Inaddition, the transceiver 2410 receives information from the processingsystem 2414, specifically the transmission component 2308, and based onthe received information, generates a signal to be applied to the one ormore antennas 2420. The processing system 2414 includes a processor 2404coupled to a computer-readable medium/memory 2406. The processor 2404 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 2406. The software, whenexecuted by the processor 2404, causes the processing system 2414 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 2406 may also be used forstoring data that is manipulated by the processor 2404 when executingsoftware. The processing system 2414 further includes at least one ofthe components 2304, 2306, 2308. The components may be softwarecomponents running in the processor 2404, resident/stored in thecomputer readable medium/memory 2406, one or more hardware componentscoupled to the processor 2404, or some combination thereof. Theprocessing system 2414 may be a component of the base station 310 andmay include the memory 376 and/or at least one of the TX processor 316,the RX processor 370, and the controller/processor 375.

In certain aspects, the apparatus 2302/2302′ for wireless communicationmay include means for determining a narrowband TDD frame structure fornarrowband communications. In one aspect, the narrowband TDD framestructure may include one or more of a set of downlink subframes, a setof uplink subframes, a set of special subframes, or a set of flexiblesubframes. In one aspect, a flexible subframe may be configurable by thebase station as either a downlink subframe or an uplink subframe. Incertain other aspects, the apparatus 2302/2302′ for wirelesscommunication may include means for transmitting a bitmap associatedwith the narrowband TDD frame structure to a UE. In one aspect, thebitmap may indicate the one or more of the set of downlink subframes,the set of uplink subframes, the set of special subframes, or the set offlexible subframes. In another aspect, a first length of the bitmapassociated with the narrowband TDD frame structure may be longer than asecond length of a different bitmap associated with a narrowband FDDframe structure. In certain aspects, the means for transmitting thebitmap associated with the narrowband TDD frame structure to a UE may beconfigured to transmit a single bitmap indicating the one or more of theset of downlink subframes, the set of uplink subframes, the set ofspecial subframes, or the set of flexible subframes. In certain aspects,the means for transmitting the bitmap associated with the narrowband TDDframe structure to a UE may be configured to transmit first informationindicating the set of downlink subframes. In certain aspects, the meansfor transmitting the bitmap associated with the narrowband TDD framestructure to a UE may be configured to transmit second informationindicating the set of uplink subframes. In certain aspects, the meansfor transmitting the bitmap associated with the narrowband TDD framestructure to a UE may be configured to transmit third informationindicating the set of special subframes. In certain aspects, the meansfor transmitting the bitmap associated with the narrowband TDD framestructure to a UE may be configured to transmit fourth informationindicating the set of flexible subframes. The aforementioned means maybe one or more of the aforementioned components of the apparatus 2302and/or the processing system 2414 of the apparatus 2302′ configured toperform the functions recited by the aforementioned means. As describedsupra, the processing system 2414 may include the TX Processor 316, theRX Processor 370, and the controller/processor 375. As such, in oneconfiguration, the aforementioned means may be the TX Processor 316, theRX Processor 370, and the controller/processor 375 configured to performthe functions recited by the aforementioned means.

FIG. 25 is a flowchart 2500 of a method of wireless communication. Themethod may be performed by a base station (e.g., the base station 102,180, 504, eNB 310, the apparatus 1102/1102′, 1302/1302′, 1502/1502′,1702/1702′, 1902/1902′, 2302/2302′). In FIG. 25, optional operations areindicated with dashed lines.

At 2502, the base station may determine a narrowband TDD frame structurefor narrowband communications from a group of narrowband TDD framestructures. For example, referring to FIGS. 5B-5D, base station 504 maydetermine 515 a narrowband TDD frame structure for the narrowbandcommunications 509 from a group of narrowband TDD frame structures(e.g., the configurations listed in table 410 in FIG. 4).

At 2504, the base station may determine a set of narrowband carriers anda minimum set of subframes on the set of narrowband carriers based atleast in part on the set of downlink subframes and more than one specialsubframe on which a NRS should be transmitted. In certain aspects, theminimum set of subframes used to transmit the NRS may not be a functionof the narrowband TDD frame structure determined for the narrowbandcommunications. In certain other aspects, the minimum set of subframesmay be restricted to subframes which are downlink subframes or specialsubframes in all supported TDD frame structures for the narrowbandcommunications. In certain other aspects, the minimum set of subframesused to transmit the NRS may be a function of the narrowband TDD framestructure determined for the narrowband communications. For example,referring to FIGS. 5B-5D, base station 504 may determine a set ofnarrowband carriers and a minimum set of subframes (e.g., the commonsubframes described above) on which the NRS 541 should be transmitted.For example, when the narrowband TDD frame structure is determined fromone of configurations 0, 1, 2, 3, 4, 5, 6, and m, the NRS 541 may besent on one of subframe 0 or subframe 5 because subframes 0 and 5 arecommon downlink subframes in each configuration in the group. Further,the NRS 541 may be sent on subframe 1 or subframe 6 because subframes 1and 6 are special subframes (e.g., that include downlink resources) ordownlink subframes in each of configuration 0, 1, 2, 3, 4, 5, 6, and m.In another example, when the narrowband TDD frame structure isdetermined from one of configurations 1, 2, 3, 4, 5, and 6, the NRS 541may be sent on one of subframe 0, subframe 5, or subframe 9 becausesubframes 0, 5, and 9 are common downlink subframes in eachconfiguration in the group. Alternatively, base station 504 may transmitthe NRS 541 in a downlink subframe that is not a function of thedetermined narrowband TDD frame structure. For example, a NPBCH 535transmitted by base station 504 may be used to indicate the downlinksubframes that include the NRS 541 to UE 506 when the downlink subframeused to transmit the NRS 541 is not a function of the determinednarrowband TDD frame structure. In certain aspects, a bitmap 539 may beincluded in NPBCH 535.

At 2506, the base station may transmit information indicating additionalsubframes used to transmit the NRS. In one aspect, the information mayinclude broadcast signaling. For example, referring to FIGS. 5B-5D, basestation 504 may transmit the NRS 541 in a downlink subframe that is nota function of the determined narrowband TDD frame structure. Forexample, a NPBCH 535 (e.g., broadcast signaling) transmitted by basestation 504 may be used to indicate the downlink subframes that includethe NRS 541 to UE 506 when the downlink subframe used to transmit theNRS 541 is not a function of the determined narrowband TDD framestructure.

At 2508, the base station may transmit a NRS using the narrowband TDDframe structure determined for the narrowband communications. In oneaspect, the NRS may be transmitted using a subframe that is also used totransmit the SIB and BCH. In another aspect, the NRS may be transmittedusing a resource block that is different than a resource block used totransmit at least one of the PSS or the SSS. In another aspect, the samesubframe used to transmit the NRS, SIB, and BCH may be not a function ofthe narrowband TDD frame structure determined for the narrowbandcommunications. In a further aspect, the same subframe used to transmitthe NRS, SIB, and BCH may be a function of the narrowband TDD framestructure determined for the narrowband communications. In anotheraspect, a density of the NRS transmitted using the narrowband TDD framestructure may be increased as compared to a density of an NRStransmitted using a narrowband FDD frame structure. In still anotheraspect, the NRS is transmitted in symbols and resource elements used totransmit a CRS. In yet a further aspect, the NRS may be transmitted in adownlink portion of a special subframe in the narrowband TDD framestructure determined for narrowband communications. In one aspect,symbols used to transmit the NRS in the downlink portion of the specialsubframe may be the same as symbols used to transmit the NRS in downlinksubframes in the narrowband TDD frame structure. In another aspect, anyNRS symbols present in an uplink portion of the special subframe may bepunctured. In a further aspect, symbols used to transmit the NRS in thedownlink portion of the special subframe may be different than symbolsused to transmit the NRS in downlink subframes in the narrowband TDDframe structure. In certain aspects, the symbols used to transmit theNRS are determined based on a number of downlink symbols in a specialsubframe configuration. For example, referring to FIGS. 5B-5D, basestation 504 may transmit a NRS 541 using the narrowband TDD framestructure determined for the narrowband communications 509. For example,base station 504 may transmit the NRS using a subframe that is also usedto transmit the SIB 537 and/or NPBCH 535. Additionally, the NRS 541 maybe transmitted using a different RB than the RB used to transmit theNPSS 521 and/or the NSSS 529. In certain aspects, base station 504 maytransmit the NRS 541 using one of the common subframes described above.For example, when the narrowband TDD frame structure is determined fromone of configurations 0, 1, 2, 3, 4, 5, 6, and m, the NRS 541 may besent on one of subframe 0 or subframe 5 because subframes 0 and 5 arecommon downlink subframes in each configuration in the group. Further,the NRS 541 may be sent on subframe 1 or subframe 6 because subframes 1and 6 are special subframes (e.g., that include downlink resources) ordownlink subframes in each configuration in the group. In anotherexample, when the narrowband TDD frame structure is determined from oneof configurations 1, 2, 3, 4, 5, and 6, the NRS 541 may be sent on oneof subframe 0, subframe 5, or subframe 9 because subframes 0, 5, and 9are common downlink subframes in each configuration in the group. TheNRS 541 may be transmitted in the DwPTS portion (e.g., see FIG. 4) of aspecial subframe and in downlink subframes in the determined narrowbandTDD frame structure. In one aspect, the same symbols in the DwPTSportion of the special subframe and the downlink subframes may be usedto transmit the NRS 541. When the NRS 541 is transmitted in the DwPTS ofthe special subframe, the UpPTS portion of the special subframe may bepunctured. In certain aspects, a density of the NRS 541 transmittedusing the narrowband TDD frame structure may be greater than an NRSdensity transmitted using a narrowband FDD frame structure. In otherconfigurations, the NRS 541 may be transmitted in symbols and resourceelements that base station 504 uses to transmit a CRS.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communications for a base station, comprising: determining a narrowband time-division duplex (TDD) frame structure for narrowband communications from a group of narrowband TDD frame structures, the narrowband TDD frame structure including a set of downlink subframes and more than one special subframe; determining a set of narrowband carriers and a minimum set of subframes on the set of narrowband carriers based at least in part on the set of downlink subframes and more than one special subframe on which a narrowband reference signal (NRS) should be transmitted; and transmitting the NRS using the narrowband TDD frame structure determined for the narrowband communications.
 2. The method of claim 1, wherein the NRS is transmitted on a carrier containing a system information block (SIB) or a broadcast channel, and wherein the minimum set of subframes includes subframes used to transmit the SIB and the BCH.
 3. The method of claim 2, wherein the minimum set of subframes used to transmit the NRS is not a function of the narrowband TDD frame structure determined for the narrowband communications, and wherein the minimum set of subframes is restricted to subframes which are downlink subframes or special subframes in all supported TDD frame structures for the narrowband communications.
 4. The method of claim 2, wherein the minimum set of subframes used to transmit the NRS is a function of the narrowband TDD frame structure determined for the narrowband communications.
 5. The method of claim 1, further comprising: transmitting information indicating additional subframes used to transmit the NRS.
 6. The method of claim 5, wherein the information includes broadcast signaling.
 7. The method of claim 1, wherein the NRS is transmitted using a first resource block that is different than a second resource block used to transmit at least one of a primary synchronization signal (PSS) or a secondary synchronization signal (SSS).
 8. The method of claim 1, wherein a density of the NRS transmitted using the narrowband TDD frame structure is increased as compared to a density of a different NRS transmitted using a narrowband frequency-division duplex (FDD) frame structure.
 9. The method of claim 8, wherein the NRS is transmitted in symbols and resource elements used to transmit a cell-specific reference signal (CRS).
 10. The method of claim 1, wherein the NRS is transmitted in a downlink portion of a special subframe in the narrowband TDD frame structure determined for narrowband communications.
 11. The method of claim 10, wherein symbols used to transmit the NRS in the downlink portion of the special subframe are also the symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 12. The method of claim 10, wherein any NRS symbols present in an uplink portion of the special subframe are punctured.
 13. The method of claim 10, wherein first symbols used to transmit the NRS in the downlink portion of the special subframe are different than second symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 14. The method of claim 10, wherein symbols used to transmit the NRS are determined based on a number of downlink symbols in a special subframe configuration.
 15. An apparatus for wireless communications for a base station, comprising: means for determining a narrowband time-division duplex (TDD) frame structure for narrowband communications from a group of narrowband TDD frame structures, the narrowband TDD frame structure including a set of downlink subframes and more than one special subframe; means for determining a set of narrowband carriers and a minimum set of subframes on the set of narrowband carriers based at least in part on the set of downlink subframes and more than one special subframe on which a narrowband reference signal (NRS) should be transmitted; and means for transmitting the NRS using the narrowband TDD frame structure determined for the narrowband communications.
 16. The apparatus of claim 15, wherein the NRS is transmitted on a carrier containing a system information block (SIB) or a broadcast channel, and wherein the minimum set of subframes includes subframes used to transmit the SIB and the BCH.
 17. The apparatus of claim 16, wherein the minimum set of subframes used to transmit the NRS is not a function of the narrowband TDD frame structure determined for the narrowband communications, and wherein the minimum set of subframes is restricted to subframes which are downlink subframes or special subframes in all supported TDD frame structures for the narrowband communications.
 18. The apparatus of claim 16, wherein the minimum set of subframes used to transmit the NRS is a function of the narrowband TDD frame structure determined for the narrowband communications.
 19. The apparatus of claim 15, further comprising: means for transmitting information indicating additional subframes used to transmit the NRS.
 20. The apparatus of claim 19, wherein the information includes broadcast signaling.
 21. The apparatus of claim 16, wherein the NRS is transmitted using a first resource block that is different than a second resource block used to transmit at least one of a primary synchronization signal (PSS) or a secondary synchronization signal (SSS).
 22. The apparatus of claim 16, wherein a density of the NRS transmitted using the narrowband TDD frame structure is increased as compared to a density of a different NRS transmitted using a narrowband frequency-division duplex (FDD) frame structure.
 23. The apparatus of claim 22, wherein the NRS is transmitted in symbols and resource elements used to transmit a cell-specific reference signal (CRS).
 24. The apparatus of claim 16, wherein the NRS is transmitted in a downlink portion of a special subframe in the narrowband TDD frame structure determined for narrowband communications.
 25. The apparatus of claim 24, wherein symbols used to transmit the NRS in the downlink portion of the special subframe are also the symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 26. The apparatus of claim 24, wherein any NRS symbols present in an uplink portion of the special subframe are punctured.
 27. The apparatus of claim 24, wherein first symbols used to transmit the NRS in the downlink portion of the special subframe are different than second symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 28. The apparatus of claim 24, wherein symbols used to transmit the NRS are determined based on a number of downlink symbols in a special subframe configuration.
 29. An apparatus wireless communications for a base station, comprising: a memory; and at least one processor coupled to the memory and configured to: determine a narrowband time-division duplex (TDD) frame structure for narrowband communications from a group of narrowband TDD frame structures, the narrowband TDD frame structure including a set of downlink subframes and more than one special subframe; determine a set of narrowband carriers and a minimum set of subframes on the set of narrowband carriers based at least in part on the set of downlink subframes and more than one special subframe on which a narrowband reference signal (NRS) should be transmitted; and transmit the NRS using the narrowband TDD frame structure determined for the narrowband communications.
 30. The apparatus of claim 29, wherein the NRS is transmitted on a carrier containing a system information block (SIB) or a broadcast channel, and wherein the minimum set of subframes includes subframes used to transmit the SIB and the BCH.
 31. The apparatus of claim 30, wherein the minimum set of subframes used to transmit the NRS is not a function of the narrowband TDD frame structure determined for the narrowband communications, and wherein the minimum set of subframes is restricted to subframes which are downlink subframes or special subframes in all supported TDD frame structures for the narrowband communications.
 32. The apparatus of claim 30, wherein the minimum set of subframes used to transmit the NRS is a function of the narrowband TDD frame structure determined for the narrowband communications.
 33. The apparatus of claim 29, wherein the at least one processor is further configured to: transmit information indicating additional subframes used to transmit the NRS.
 34. The apparatus of claim 33, wherein the information includes broadcast signaling.
 35. The apparatus of claim 29, wherein the NRS is transmitted using a first resource block that is different than a second resource block used to transmit at least one of a primary synchronization signal (PSS) or a secondary synchronization signal (SSS).
 36. The apparatus of claim 29, wherein a density of the NRS transmitted using the narrowband TDD frame structure is increased as compared to a density of a different NRS transmitted using a narrowband frequency-division duplex (FDD) frame structure.
 37. The apparatus of claim 36, wherein the NRS is transmitted in symbols and resource elements used to transmit a cell-specific reference signal (CRS).
 38. The apparatus of claim 29, wherein the NRS is transmitted in a downlink portion of a special subframe in the narrowband TDD frame structure determined for narrowband communications.
 39. The apparatus of claim 38, wherein symbols used to transmit the NRS in the downlink portion of the special subframe are also the symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 40. The apparatus of claim 38, wherein any NRS symbols present in an uplink portion of the special subframe are punctured.
 41. The apparatus of claim 38, wherein first symbols used to transmit the NRS in the downlink portion of the special subframe are different than second symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 42. The apparatus of claim 38, wherein symbols used to transmit the NRS are determined based on a number of downlink symbols in a special subframe configuration.
 43. A computer-readable medium storing computer executable code for a base station, comprising code to: determine a narrowband time-division duplex (TDD) frame structure for narrowband communications from a group of narrowband TDD frame structures, the narrowband TDD frame structure including a set of downlink subframes and more than one special subframe; determine a set of narrowband carriers and a minimum set of subframes on the set of narrowband carriers based at least in part on the set of downlink subframes and more than one special subframe on which a narrowband reference signal (NRS) should be transmitted; and transmit the NRS using the narrowband TDD frame structure determined for the narrowband communications.
 44. The computer-readable medium of claim 43, wherein the NRS is transmitted on a carrier containing a system information block (SIB) or a broadcast channel, and wherein the minimum set of subframes includes subframes used to transmit the SIB and the BCH.
 45. The computer-readable medium of claim 44, wherein the minimum set of subframes used to transmit the NRS is not a function of the narrowband TDD frame structure determined for the narrowband communications, and wherein the minimum set of subframes is restricted to subframes which are downlink subframes or special subframes in all supported TDD frame structures for the narrowband communications.
 46. The computer-readable medium of claim 44, wherein the minimum set of subframes used to transmit the NRS is a function of the narrowband TDD frame structure determined for the narrowband communications.
 47. The computer-readable medium of claim 43, further comprising code to: transmit information indicating additional subframes used to transmit the NRS.
 48. The computer-readable medium of claim 47, wherein the information includes broadcast signaling.
 49. The computer-readable medium of claim 43, wherein the NRS is transmitted using a first resource block that is different than a second resource block used to transmit at least one of a primary synchronization signal (PSS) or a secondary synchronization signal (SSS).
 50. The computer-readable medium of claim 43, wherein a density of the NRS transmitted using the narrowband TDD frame structure is increased as compared to a density of a different NRS transmitted using a narrowband frequency-division duplex (FDD) frame structure.
 51. The computer-readable medium of claim 50, wherein the NRS is transmitted in symbols and resource elements used to transmit a cell-specific reference signal (CRS).
 52. The computer-readable medium of claim 43, wherein the NRS is transmitted in a downlink portion of a special subframe in the narrowband TDD frame structure determined for narrowband communications.
 53. The computer-readable medium of claim 52, wherein symbols used to transmit the NRS in the downlink portion of the special subframe are also the symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 54. The computer-readable medium of claim 52, wherein any NRS symbols present in an uplink portion of the special subframe are punctured.
 55. The computer-readable medium of claim 52, wherein first symbols used to transmit the NRS in the downlink portion of the special subframe are different than second symbols used to transmit the NRS in downlink subframes in the narrowband TDD frame structure.
 56. The computer-readable medium of claim 52, wherein symbols used to transmit the NRS are determined based on a number of downlink symbols in a special subframe configuration. 